The origin of species by means of natural selection, or, The preservation of favoured races in the struggle for life

LIBRARY
Brigham Young University

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144241

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J?f4 ,

)c>00 THE

OEIGIN OF SPECIES

BY MEANS OF NATURAL SELECTION,

OR THE

£. 3RYATI0N OP FAVOURED RACES IN THE STRUGGLE

FOR LIFE.

By CHAELES DAEWIN, M.A., LL.D., F.E.S.

giXTH EDITION, WITH ADDITIONS AND CORREvIIONe TO 187^'.

(JHIRTY'FIFTn THOUSAND.) ','^ ,',

3.3 •> ^

LONDON:

jqHN mueeay, albemaele street.

1888.

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" But with regard to the material world, we can at least go so far as
this — we can perceive that events are brought about not by insulated
interpositions of Divine power, exerted in each particular case, but bj" the
establishment of general laws." Wf

Whewell: Bridgewater Treatise. |

" The only distinct meaning of the word 'natural* is stated, fixed, or \
settled ; since what is natural as much requires and presupposes an intel-
ligent agent to render it so, i. <?., to effect it continually or at stated times,
as what is supernatural or miraculous does to effect it for once."

BuTLEH : Analogy of Eeveakd Beltgion.

" To conclude, therefore, let no man out of a weak conceit of sobriety, j
or an ill-applied moderation, think or maintain, that a man can search too \
far or be too well studied in the book of God's word, or in the book of (
God's works ; divinity or philosophy ; but rather let men endeavour ns '
endless progress or proficience in both." )

Bacon : Advancement of Learning. ^

Dcwn, Beckenham, Kent,

First Edition, November 26ih, I860,
Sixtit JEdition, Jan, 1872.

CONTENTS.

Additions and Corrections, to the Sixin EDiTioy .. Page xi-xii

HisTOKiCAL Sketch xiii-xxi

Introduction.. 1-4

CHAPTER I.

Variation under Domestication.

Causes of Variability — Effects of Habit and the use or disute of Parts —
' Correlated Variation — Inheritance — Character of Domestic Varieties
— Difficulty of distinguishing between Varieties and Species — Origin
of Domestic Varieties from one or more Species — Domestic Pigeons,
their Differences and Origin — Principles of Selection, anciently fol-
lowed, their Effects — Methodical and Unconscious Selection — Un-
knov/n Origin of our Domestic Productions — Circumstances favour-
able to Man's power of Selection 5-32

CHAPTER II.

Variation under Nature.

Variability —- Individual differences — Doubtful species — Wide ranging,
much diffused, and common species, vary most — Species of the large:
genera in each country vary more fiequently than the species of the
smaller genera — Many of the species of the larger genera resembk
varieties in being very closely, but unequally, related to each other,
and in having restricted ranges 33-47

CHAPTER III.

Struggle for Existence.

Its bearing on natural selection — The term used in a wide sense — Geome-
trical ratio of increase — Rapid increase of naturalised animals and
plants — Nature of the checks to increase — Competition universal —
Effects of climate — Protection from the number of individuals —
Complex relations of all animals and plants throughout nature —
Struggle for life most severe between individuals and varieties of th<
same species : often severe between species of the same genus — The
relation of organism to ovganisTi the most important of all rela-
tions 48-61

VI CONTENTS.

/

CHAPTER lY.

Natural Selection; or the Survival of the Ffi'test.

Natural Selection — its power compared with man's selection — its power
on characters of trifling importance — its power at all ages and on both
sexes — Sexual Selection — On the generality of intercrosses between
individuals of the same species — Circumstances favourable and unfa-
vourable to the results of Natural Selection, namely, intercrossing,
isolation, number of individuals — Slow action — Extinction caused by
Natural Selection — Divergence of Character, related to the diversity of
inhabitants of any small area, and to naturalisation — Action of Natural
Selection, through Divergence of Character and Extinction, on the
descendants from a common parent — Explains the grouping of all
organic beings — Advance in organisation — Low forms preserved
— Convergence of character — Indefinite multiplication of species —
Summary P'^g<^ 62-105

CHAPTER V.

Laws of Variation.

Effects of changed conditions — Use and disuse, combined with natTiral
selection ; organs of flight and of vision — Acclimatisation — Correlated
variation — Compensation and economy of growth — False correlations i
— Multiple, rudimentary, and lowly organised structures variable — ■ J
Parts developed in an unusual manner are highly variable : specific
characters more variable than generic : secondary sexual characters
variable — Species of the same genus vary in an analogous manner —
Rerersions to long-lost characters — Summary 106-132

CHAPTER VI.

Difficulties of the Theory.

Difliculties of the theory of descent with modification — Absence or rarity
of transitional varieties — Transitions in habits of life — Diversified
habits in the same species — Species with habits widely difierent
from those of their allies — Organs of extreme perfection — Modes of
transition — Cases of difficulty — Natura non facit saltum — Organs ■
of small importance — Organs not in all cases absolutely perfect — I
The law of Unity of Type and of the Conditions of Existence embraced
by the tlicory of Natural Se'-ection .. .. c. .. .. locJ-167

CONTENTS. ''"11

CHAPTER VIL

Miscellaneous Objections to the Theory of Natural

Selection.

Longevity — Modifications not necessarily simultaneous — Modification*
apparently of no direct service — Progressive development — Characters
of small functional importance, the most constant — Supposed incom-
petence of natural selection to account for the incipient stages ot
useful structures — Causes which interfere with the acquisition through
natural selection of useful structures — Gradations of structure with
changed functions — Widely different organs in members of the same
class, developed from one and the same source — Reasons for disbeliev-
ing in great and abrupt modi£cations Page 168-204

CHAPTEE VIII.

Instinct.

Instincts comparable with habits, but different in their origin — Instincts
graduated — Aphides and ants — Instincts variable — Domestic in-
stincts, their origin — Natural instincts of the cuckoo, molothrus,
ostrich, and parasitic bees — Slave-making ants — Hive-bee, its cell-
making instinct — Changes of instinct and structure not necessarily
simultaneous — Difficulties of the theory of the Natural Selection of
instincts — Neuter or sterile insects — Summary .. .. 205-234

CHAPTEE IX.

Hybridism.

Distinction betweon the sterility of first crosses and of hybrids — Sterility
various in degree, not universal, affected by close interbreeding, re-
moved by domestication — Laws governing the sterility of hybrids — ■
Sterility not a special endowment, but incidental on other differences,
not accumulated by natural selection — Causes of the sterility of first
crosses and of hybrids — Parallelism between the effects of changed
conditions of life and of crossing — Dimorphism and Trimorphism —
Fertility of va-rieties when crossed and of their mongrel offspring not
Tiniversal — Hybrids and mongrels compared independently of their
fertility — Summary 234-263

VIU CONTENTS.

CHAPTER X.

On the Imperfectiox of the Geological Recoud.

Ou the absence of intermedir-te varieties at the present day — On the
nature of extinct intermediate varieties ; on their number — On
the lapse of time, as inferred from the rate of denudation and ot
deposition — On the lapse ci time as estimated by years — On the
poorness of our palaeontological collections — On the intermittence of
geological formations — On the denudation of granitic areas — On the
absence of intermediate varieties in any one formation — On the sudden
appearance of groups of species — On their sudden appearance in
the lowest known fossiliferous strata — Antiquity of the habitable
earth Page 264-28S

-^ ^ , CHAPTER XL

On the Geological Succession of Organic Beings.

On the slow and successire appearance of new species — On their different
rates of change — Speciesonce lost do-tiot-'reflppear — Groups of species
follow the same general rules in their appearance and disappearance
as do single species — On Extinction — On simultaneous changes in
the forms of life throughout the world — On the affinities of extinct
species to each other and to living species — On the state of develop-
ment of ancient forms — On the succession of the same types within
the same areas — Summary of preceding and present chapter 290-315

CHAPTER XII.

Geographical Distribution.

Ptvsent distribution cannot be accounted for by differences in physical
conditions — Importance of barriers — AfTmity of the productions of
the same continent — Centres of creation — Means of dispersal, by
changes of climate and of the level of the laud, and by occasional means
— Dispersal during the Glacial period — Alternate Glacial periods in
the north and south 316-342

CHAPTER XIII.

Geographical Distribution — continued.

Distribution of fresh-water productions — On the inhabitants of oceanic
islands — Absence of Batrachians and of terrestrial Mammals — On
the relation of the inhabitants of islands to those of the nearest main-
land — On colonization from the nearest source with subsequent modi-
fication— Summary of the last and present chapter .. .. 343-802

CONTENTS. LI

CnAPTEE XIV.

Mutual Affinities of Organic Beings: Morphology:
Embryology : Kudimentary Organs.

Classification, groups subordinate to groups — JJftUuaX system — Rules
and difficulties in classification, explained on the theory of descent
with modification — Classification of varieties — Descent always used
in classification — Analogical or adaptive characters — Affinities,
general, complex, and radiating — Extinction separates and defines
groups — MctRPHOLOGY, between members of the same class, between
parts of the same individual — Embryology, laws of, explained by
T'ariations not supervening at an early age, and being inherited at a
corresponding age — Rudimentary organs ; their origin explained —
Summary Page 363-403

CHAPTER XV.

PiECAriTULATlON AND CONCLUSION.

Recapitulation of the objections to the theary of Natural Selection —
Recapitulation of the general and special circumstances in its favour
. — Causes of the general belief in the immutability of species —
How far the theory of Natural Selection may be extended —
Effects of its adoption on the study of Natural History — Con-
cluding remarks 404—429

Glossary of Scientific TEiora 430

Injsx ,, 44a

INSTRUCTION TO BINDER.

The Diagram to front page 90, and to face the latter part of the Volume,

ADDITIONS AND CORRECTIONS

TO THE SIXTH EDITION.

-•o*-

Numerous small corrections have been made in tlie last
and present editions on various subjects, according as the
evidence has become somewhat stronger or weaker. The
more important corrections and some additions in the pre-
sent volume are tabulated on the following page, for the
convenience of those interested in the subject, and who
possess the fifth edition. JThe second edition was little
more than a reprint of the first. The third edition was
largely corrected and added to, and the fourth and fifth
still more largely. As copies of the present work will
be sent abroad, it may be of use if I specify the state of
the foreign editions. The third French and second Ger-
man editions were from the third English, with some few
of the additions given in the fourth edition. x\ new fourth
French edition has been translated by Colonel Moulinie ;
of which the first half is from the fifth English, and the
latter half from the present edition. A third German
edition, under the superintendence of Professor Victor
Cams, was from the fourth English edition ; a fifth is now
preparing by the same author from the present volume.
The second American edition was from the English second,
with a few of the additions given in the third; and a
third American edition has been printed from the fifth
English edition. The Italian is from the third, the Dutch
and three Eussian editions from the second English edition,
and the Swedish from the fifth English edition.

Xll

ADDITIONS AND CORRECTIONS.

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Chief Additions and Corrections.

Influence of fortuitous destruction on natural selection

On the convergence of specific forms.

Account of the Ground-Woodpecker of La Plata modified.

On tlie modification of the eye.

Transitions through the acceleration or retardation of the
period of reproduction.

The account of the electric organ of fishes added to.

Analogical resemblance between the eyes of Cephalopoda
and Vertebi'ates.

Chaparede on the analogical resemblance of the hair-clasp«rs
of the Acaridff"..

The probable use of the rattle to the Rattle-snake.

Helmholtz on the imperfection of the human eye.

The first part of this new chapter consists of portions, in a
much modified state, taken from chap. iv. of the former
editions. The latter and larger part is new, and relates
chiefly to the supposed incompetency of natural selection
to account for the incipient stages of useful structures.
There is also a discussion on the causes which prevent
in many cases the acquisition through natural selection
of useful structures. Lastly, reasons are given for dis-
believing in great and sudden modifications. Gradations
of character, often accompanied by changes of function,
are likewise here incidentally considei^.

The statement with respect to young cuckoos ejecting their
foster-brothers confirmed.

On the cuckoo-like habits of the Molothrus.

On fertile hybrid moths.

The discussion on the fertility of hybrids not having been ac-
quired through natural selection condensed and modified.

On the causes of sterility of hybrids, added to and correctetL

Pyrgoma found in the chalk.

Extinct forms serving to connect existing groups.

On earth adhering to the feet of migratory birds.

On the wide geographical range of a species of Galaxias,
a fresh-water fish.

Discussion on analogical resemblances, enlarged and modified

Homological structure of the feet of certain marsupial
animals.

On serial homologies, corrected.

Mr. E. Ray Lankester on morphology.

On the asexual reproduction of Chironomus.

On the origin of rudimentary parts, corrected.

Recapitulation on the sterility of hybrids, corrected.

Recapitulation on the absence of fossils beneath the Cani-
brian system, corrected.

Natural selection not the exclusive agency in the modi-
fication of species, as always maintained in this work

The belief in the separate creation of species ^^enei'ally held
by naturalists, until a recent period.

AN HISTORICAL SKETCH

OF THE PROGRESS OF OPINION ON THE ORIGIN OF SPECIKS,

FREnOUSLY TO THE PUBLICATION OF THE FIRST EDITION
OP THIS WORK.

I WILL here a give a brief sketch of the progress of opinion on tne
Origin of Species. Until recently the great majority of naturalists
believed that species were immutable i^rouuctions, and had been
separately created. This view has been ably maintained by many
authors. Some few naturalists, on the other hand, have believed
that species undergo modification, and that the existing forms of
life are the descendants by true generation of pre-existing forms.
Passing over allusions to the subject in the classical writers,* the first
author who in modern times has treated it in a scientific spirit was
Buffon. But as his opinions fluctuated greatly at different periods,
and as he does not enter on the causes or means of the transforma-
tion of species, I need not here enter on details.

Lamarck was the first man whose conclusions on the subject
excited much attention. This justly-celebrated naturalist first pub-
lished his views in 1801 ; he much enlarged them in 1809 in his
* Philosophic Zoologique,' and subsequently, in 1815, in the Intro-
duction to his * Hist. Nat. des Animaux sans Vertebres.' In these

♦ Aristotle, in his ' Physicce Auscultationes * (lib. 2, cap. 8, s, 2), after
remarking that rain does not fall in order to make the corn grow, any
more than it falls to spoil the farmer's corn when threshed out of doors,
applies the same argument to organisation; and adds (as tianslated by
Mr. Clair Grece, who first pointed out the passage to me), " So what hinders
; the different parts [of the body] from having this merely accidental relation
/ in nature ? as the teeth, for example, grow by necessity, the front ones
/ sharp, adapted for dividing, and the grinders flat, and serviceable for mas-
ticating the food ; since they were not made for the sake of this, but it
n'as the result of accident. And in like manner as to the other parts in
which there appears to exist an adaptation to an end. Whei'esoever, there-
fore, all things together (that is all the parts of one whole) happened like
as if they were made for the sake of something, these were preserved,
having been appropriately constituted by an internal spontaneity ; and
i whatsoever things wore not thus constituted, perished, and still perish."
We here see the principle of natural selection shadowed forth, but how
little Aristotle fully comprehended the principle, is shown by his remarks
on the formation of the teeth.

Xiv HISTORICAL SKETCH.

works he upholds the doctrine that all species, including man, are
descended from other species. He first did the eminent service of
arousing attention to the probability of all change in the organic, as
well as in the inorganic world, being the result of law, and not of
j_miraculous interposition. Lamarck seems to have been chiefly led
to his conclusion on the gradual change of species, by the difficulty
of distinguishing species and varieties, by the almost perfect gradation
of forms in certain groups, and by the analogy of domestic produc-
tions. With resp,ect to the means of modification, he attributed
something to the direct action of the physical conditions of life,
something to the crossing of already existing forms, and much to use
and disuse, that is, to the effects of habit. To this latter agency he
seems to attribute all the beautiful adaptations in nature ; — such as
the long neck of the girafi'e for browsing on the branches of trees.
But he likewise believed in a law of progressive development ; and
as all the forms of life thus tend to progress, in order to account for
the existence at the present day of simple productions, he maintains
that such forms are now spontaneously generated.*

Geoffrey Saint Hilaire, as is stated in his ' Life,' written by his
son, suspected, as early as 1795, that what we call species are
various degenerations of the same type. It was not until 1828
that he published his conviction that the same forms have not been
perpetuated since the origin of all things. Geoffrey seems to have
relied chiefly on the conditions of life, or the " monde ambiant " as
the cause of change. He was cautious in drawing conclusions, and
did not believe that existing species are now undergoing modifica-
tion ; and, as his son adds, " C'est done un problem e k reserver
entierement h I'avenir, suppose meme que I'avenir doive avoir prise
sur lui."

* I have taken the date of the first publication of Lamarck from Isid.
(jteoffroy Saint Hilaire's (' Hist. Nat. Ge'nerale,' torn, ii. p. 405, 1859) excel-
lent history of opinion on this subject. In this work a full account is given
of Buffon's conclusions on the same subject. It is curious how largely my
grandfather, Dr. Erasmus Darwin, anticipated the views and erroneous
grounds of opinion of Lamarck in his ' Zoonomia ' (vol. i. pp. 500-510),
published in 1794. According to Isid. Geoffroy there is no doubt that
Goethe was an extreme partisan of similar views, as shown in the Intro-
duction to a work written m 1794 and 1795, but not published till long
afterAvards : he has pointedly remarked (' Goethe als Naturforscher,' von
Dr. Karl Meding, s. 34) that the future question for naturalists will be how,
for instance, cattle got their horns, and not for what they are used. It is
rather a singular instance of the manner in which similar views arise at
about the same time, that Goethe in Germany, Dr. D -win in England,
and Geoffroy Saint Hilaire (as we shaU immediately se^^ in France, came
to the same conclusion on the origin of species, in the years 1794-5.

HISTORICAL SKETCH. i^

In 1813, Dr. W. C. Wells read before the L'oyal Society ' An
Account of a White Female, part of whose skin resembles that of
a Negro ' ; but his paper was not published until his famous * Two
Essays upon Dew and Single Vision ' appeared in 1818. In this
paper he distinctly recognises the principle of natural selection, and
this is the first recognition which has been indicated ; but he applies
it only to the races of man, and to certain characters alone. After
remarking that negroes and mulattoes enjoy an immunity from
certain tropical diseases, he observes, firstly, that all animals tend to
vary in some degree, and, secondly, that agriculturists improve their
domesticated animals by selection ; and then, he adds, but what is
done in this latter case " by art, seems to be done with equal efiicacy,
though more slowl}'', by nature, in the formation of varieties of
mankind, fitted for the country which they inhabit Of the acci-
dental varieties of man, which would occur among the first few and
scattered inhabitants of the middle regions of Africa, some one
would be better fitted than the others to bear the diseases of the
country. This race would consequently multiply, while the others
would decrease ; not only from their inability to sustain the attacks
of disease, but from their incapacity of contending with their more
vigorous neighbours. The colour of this vigorous race I talse for
granted, from what has been already said, would be dark. But the
same disposition to form varieties still existing, a darker and a
darker race would in the course of time occur : and as the darkest
would be the best fitted for the climate, this would at length
become the most prevalent, if not the only race, in the particular
country in which it had originated." He then extends these same
views to the white inhabitants of colder climates. I am indebted
to Mr. Rowley, of the United States, for having called my atten-
tion, through Mr. Brace, to the above passage in Dr. Well's A\-ork.

The Hon. and Eev. W. Herbert, afterwards Dean of Manchester,
in the fourth volume of the * Horticultural Transactions,' 1822, and
in his work on the ' Amaryllidaceas ' (1837, p. 19, 339), declares that
" horticultural experiments have established, beyond the possibility
of refutation, that botanical species are only a higher and more per-
manent class of varieties." He extends the same view to animals.
The Dean believes that single species of each genus were created
in an originally highly plastic condition, and that these have
produced, chiefly by intercrossing, but likewise by variation, all
our existing species.

In 1826 Professor Grant, in the concluding paragraph in his
u-ell known ^'iper (' Edinburgh Philosophical Journal,' vol. xiv.
p. 283) on the Spongilla, clearly declares his belief that, species are

JtVl HISTORICAL SKETCH.

descended from other species, and that the} become improred In
the course of modification. This same view A^as given in his 55 lb
Lecture, published in the ' Lancet ' in 1834.

In 1831 Mr. Patricia Matthew published his work on * Naval
Timber and Arboriculture,' in which he gives precisely the same
view on the origin of species as that (presently to be alluded to)
propounded by Mr. Wallace and myself in the ' Linnean Journal,
and as that enlarged in the present volume. Unfortunately the
view was given by Mr. Matthew very briefly in scattered passages
in an Appendix to a work on a different subject, so that it remained
unnoticed until Mr. Matthew himself drew attention to it in the
* Gardeners' Chronicle,' on April 7th, 1860. The differences of Mr.
Matthew's view from mine are not of much importance : he seems
to consider that the world was nearly depopulated at successive
periods, and then re-stocked ; and he gives as an alternative, that
new forms may be generated " without the presence of any mould
or germ of former aggregates." I am not sure that I understand
some passages ; but it seems that he attributes much influence to
the direct action of the conditions of life. He clearly saw, how-
ever, the full force of the principle of natural selection.

The celebrated geologist and naturalist. Von Buch, in his ex-
cellent * Description Physique des Isles Canaries ' (1836, p. 147),
clearly expresses his belief that varieties slowly become changed
into permanent species, which are no longer capable of inter-
crossing.

Eafinesque, in his ' New Flora of North America,' published in
1836, wrote (p. 6) as follows: — "All species might have been
varieties once, and many varieties are gradually becoming species
by assuming constant and peculiar characters ; " but farther on
(p. 18) he adds, "except the original types or ancestors of the
genus."

In 1843-44 Professor Haldeman (' Boston Journal of Nat. Hist.
U. States,' vol. iv. p. 468) has ably given the arguments for and
against the hypothesis of the development and modification of
species : he seems to lean towards the side of change.

The ' Vestiges of Creation ' appeared in 1844. In the tenth
and much improved edition (1853) the anonymous author says
(p. 155): — The proposition determined on after much considera-
tion is, that the several series of animated beings, from the simplest
and oldest up t:. the highest and most recent, are, under the provi-
dence of God, the results, Jirstf of an impulse which has been
imparted to the forms of life, advancing them, in definite times, by
generation, through grades of oi'ganisation terminating in the

HISTOKICAL SKETCH. XT13

highest dicotyledons and vertcbrata, these grades being few in
DU"">ber, and generally marked by intervals of organic character,
which we find to be a practical difficulty in ascertaining affinities ;
second, of another impulse connected with the vital forces, tending,
in the course of generations, to modify organic structures in accor-
dance with external circumstances, as food, the nature of the
habitat, and the meteoric agencies, these being the ' adaptations '
of the natural theologian." The author apparently believes that
organisation progresses by sudden leaps, but that the effects
produced by the conditions of life are gradual. He argues with
much force on general grounds that species are not immutable
productions. But I cannot see how the two supposed " impulses "
account in a scientific sense for the numerous and beautiful co-
adaptations which we see throughout nature ; I cannot see that we
thus gain any insight how, for instance, a woodpecker has become
adapted to its peculiar habits of life. The work, from its powerful
and brilliant style, though displaying in the earlier editions little
accurate knowledge and a great want of scientific caution, imme-
diately had a very wide circulation. In my opinion it has done
excellent service in this country in calling attention to the sub-
ject, in removing prejudice, and in thus preparing the ground
for the reception of analogous views.

In 1846 the veteran geologist M. J. d'Omalius d'Halloy pub-
lished in an excellent though short paper (* Bulletins de I'Acnd. Koy.
Bruxelles,' tom. xiii. p. 581), his opinion that it is more probable
that new species have been produced by descent with modification
than that they have been separately created : the author first
promulgated this opinion in 1831.

Professor Owen, in 1849 (' Nature of Limbs,' p. 86), wrote as
follows : — " The archetypal idea was manifested in the flesh under
diverse such modifications, upon this planet, long prior to the
existence of those animal species that actually exemplify it. To
what natural laws or secondary causes the orderly succession and
progression of such organic phenomena may have been committed^
we, as yet, are ignorant." In his Address to the British Association,
in 1858, he speaks (p. li.) of "the axiom of the continuous
operation of creative power, or of the ordained becoming of living
things." Farther on (p. xc), after referring to geograpliical distri-
bution, he adds, " These phenomena shake our confidence in the
conclusion that the Apteryx of New Zealand and the Red Grouse
of England were distinct creations in and for those islands resj^oc-
tively. Always, also, it may be well to bear in mind that by the
word 'creation' the zoologist means *a process he knows net

XVni HISTORICAL SKETCH.

what.' " He amplifies tliis idea by adding, that when snch cases
as that of the Red Grouse are " enumerated "by the zoologist as
evidence of distinct creation of the bird in and for such islands, he
chiefly expresses that he knows not how the Eed Grouse came to
be there, and there exclusively ; signifying also, by this mode of
expressing such ignorance, his belief that both the bird and the
islands owed their origin to a great first Creative Cause." If we
interpret these sentences given in the same Address, one by the
other, it appears that this eminent philosopher felt in 1858 his con-
fidence shaken that the Apteryx and the Red Grouse first appeared
in their respective homes, " he knew not how," or by some process
"he knew not what."

This Address was delivered after the papers, by Mr. Wallace and
myself on the Origin of Species, presently to be referred to, had been
read before the Linnean Society. When the first edition of this
work was published, I was so completely deceived, as were many
others, by such expressions as ** the continuous operation of creative
j30wer," that I included Professor Owen with other palcBontologists
as being firmly convinced of the immutability of species ; but it
appears ('Anat. of Vertebrates,' vol. iii. p. 79G) that this was on
my part a preposterous error. In the last edition of this work I
inferred, and the inference still seems to me perfectly just, from a
passage beginning with the words " no doubt the type-form," &c.
(Ibid. vol. i. p. XXXV.), that Professor Owen admitted that natural
selection may have done something in the formation of new
species ; but this it appears (Ibid. vol. iii. p. 798) is inaccurate and
without evidence. I also gave some extracts from a correspondenco
between Professor Owen and the Editor of the * London Review,'
from which it appeared manifest to the Editor as well as to myself,
that Professor Owen claimed to have promulgated the theory of
natural selection before I had done so ; and I expressed my surprise J
and satisfaction at this announcement ; but as far as it is possible *
to understand certain recently published passages (Ibid. vol. iii.
p. 798), I have either partially or wholly again fallen into error. hI

It is consolatory to me that others find Professor Owen's controver-
sial writings as difficult to understand and to reconcile with each
other, as I do. As far as the mere enunciation of the principle of
natural selection is concerned, it is quite immaterial whether or
not Professor Owen preceded me, for both of us, as shown in this
historical sketch, were long ago preceded by Dr. Wells and Mr.
Matthews.

M. Isidore Geoffrey Saint Hilaire, in his Lectures delivered in
LSoO (of which a Resume appeared in the ' Revue et Mag. be '

i

HISTORICAL SKETCH. xix

Zoolog.,' Jan. 1851), briefly gives his reason for believing that
specific characters " sont fixes, pour chaque espece, tant qu'elle se
perpetue au milieu des memes circonstances : ils se modifient, si
les circonstances ambiantes viennent k changer." " En resume,
Vobservation des animaux sauvages ddmontre dejk la variabilite
limitee des espfeces. Les experiences sur les animaux sauvages
devenus domestiques, et sur les animaux domestiques redevenus
sauvages, la de'montrent plus clairement encore. Ces mSmes exp(?-
riences prouvent, de plus, que les difi'^rences produites peuvent etro
de valeur genert'que''' In his * Hist. Nat. Generale ' (torn. ii. p.
430, 1859) he amplifies analogous conclusions.

From a circular lately issued it appears that Dr. Freke, in 1851
(* Dublin Medical Press,' p. 322), propounded the doctrine that all
organic beings have descended from one primordial form. His
grounds of belief and treatment of the subject are wholly different
from mine ; but as Dr. Freke has now (1861) published his Essay
on * the Origin of Species by means of Organic Affinity,' the diffi-
cult attempt to give any idea of his views would be superfluous
on my part.

Mr. Herbert Spencer, in an Essay (originally published in the
* Leader,' March 1852, and republished in his * Essays ' in 1858),
has contrasted the theories of the Creation and the Development
of organic beings with remarkable skill and force. He argues
from the analogy of domestic productions, from the changes which
the embryos of many species undergo, from the difiiculty of dis-
tinguishing species and varieties, and from the principle of general
gradation, that species have been modified ; and he attributes the
modification to the change of circumstances. The author (1855)
has also treated Psychology on the principle of the necessary
acquirement of each mental power and capacity by gradation.

In 185^ M. Naudin, a distinguished botanist, expressly stated,
in an admirable paper on the Origin of Species (' Revue Horticole,
p. 102 ; since partly republished in the * Nouvelles Archives du
Museum,' tom. i. p. 171), his belief that species are formed in
an analogous manner as varieties are under cultivation ; and the
latter process he attributes to man's power of selection. But he
does not show how selection acts under nature. He believes, like
Dean Herbert, that species, when nascent, were more plastic than at
present. He lays weight on what he calls the principle of finality,
** puissance myst^rieuse, indetermin^e ; fatalite pour les uns ; pour
les autres, volonte providentielle, dont Taction incessante sur les
§tres vivants determine, k toutes les ^poques de I'existence du
monde, la forme, le volume, et la dur^e de chacun d'eux, en raison

x:X HISTORICAL SKETCH.

I

de sa destin^e dans Tordre de choscs dont il fait par tie. C'est cette
puissance qui harmonise chaque membre k I'ensemble en I'appro-
priant a la fonction qu'il doit remplir dans I'organisme general de
la nature, fonction qui est pour lui sa raison d'etre." *

In 1853 a celebrated geologist, Count Keyserling ('Bulletin do
la Soc. Geolog.,' 2nd Ser., torn. x. p. 357), suggested that as new
diseases, supposed to have been caused by some miasma, have
arisen and spread over the world, so at certain periods the germs
of existing species may have been chemically affected by circum-
ambient molecules of a particular nature, and thus have given
rise to new forms.

In this same year, i853, Dr, Schaaffhausen published an ex-
cellent pamphlet ('Yerhand. des Naturhist. Vereins der Preuss.
Rheinlands,' &c.), in which he maintains the progressive develop-
ment of organic forms on the earth. He infers that many species
have kept true for long periods, whereas a few have become modi-
fied. The distinction of species he explains by the destruction
of intermediate graduated forms. " Thus living plants and animals
are not separated from the extinct by new creations, but are to
be regarded as their descendants through continued reproduction."

A well-known French botanist, M. Lccoq, writes in 1854
(' Etudes sur Olograph. Bot.,' tom. 1. p. 250), " On voit que nos
recherches sur la fixite ou la variation de I'esp^ce, nous conduisent
directement aux idees dmises, par deux hommes justement cel^bres,
Geoffrey Saint-Hilaire et Goethe." Some other passages scattered
through M. Lecoq's large work, make it a little doubtful how far he
extends his views on the modification of species.

The * Philosophy of Creation * has been treated in a masterly
manner by the Kev. Baden Powell, in his * Essays on the Unity of
Worlds,' 1855. Nothing can be more striking than the manner in
which he shows that the introduction of new species is " a regular,

* From references in Bronn's ' Untersuchuagen iiber die Entwiclceiungs-
Gesetze,' it appears that the celebrated botanist and paleontologist Unger
published, in 1852, his belief that species undergo development and modifi-
cation. D'Alton, likewise, in Pander and Dalton's work on Fossil Sloths,
expressed, in 1821, a similar belief. Similar views have, as is well known,
been maintained by Oken in his mystical ' Natur-Philosophie.' From other
references in Godron's work ' Sur I'Espfece,' it seems that Bory St. Vincent,
Burdach, Poiret, and Fries, have all admitted that new species are continu-
ally being produced.

I may add, that of the thirty-four authors named in this Historical
Sketch, who believe in the modification of species, or at least disbelieve in
separate acts of creation, twenty-seven have written on special branches oj
natural history or geology.

mSTORICAL SKETCH. Xxi

not a casual phenomenon," or, as Sir John Herschel expresses it,
*'a natural in contradistinction to a miraculous process."

The thii'd volume of the ' Journal of the Linnean Society ' con-
tains papers, read July 1st, 1858, by Mr. Wallace and myself, in
which, as stated in the introductory remarks to this volume, the
theory of Natural Selection is promulgated by Mr. Wallace with
admirable force and clearness.

Yon Baer, towards whom all zoologists feel so profound a respect,
expressed about the year 1859 (sec Trof. Rudolph Wagner, * Zoolo-
gisch-Anthropologische Untersuchungen,' 1861, s. 51) his convic-
tion, chiefly grounded on the laws of geographical distribution,
that forms now perfectly distinct have descended from a single
parent- form.

In June, 1859, Professor Huxley gave a lecture before the Eoyal
Institution on the * Persistent Types of Animal life.' Referring to
such cases, he remarks, " It is difficult to comprehend the meaning
of such fiicts as these, if we suppose that each species of animal
and plant J or each great type of organisation, was formed and
placed upon the surface of the globe at long intervals by a distinct
act of creative power; and it is well to recollect that such an
assumption is as unsupported by tradition or revelation as it is
opposed to the general analogy of nature. If, on the other hand,
we view * Persistent Types ' in relation to that hypothesis which
supposes the species living at any time to be the result of the
gradual modification of pre-existing species — a hypothesis which,
though unproven, and sadly damaged by some of its supporters,
is yet the only one to which physiology lends any countenance ;
their existence would seem to show that the amount of modification
■,vhich living beings have undergone during geological time is but
veiy small in relation to the whole series of changes which they
have suffered."

In December, 1859, Dr. Hooker published his ' Introduction to
the Australian Flora.' In the first part of this great work he admits
the truth of the descent and modification of species, and supports
this doctrine by many original observations.

The first edition of this work was published on November 24 th,
1859, and the second edition on Januar}" 7tb, 18G0.

d

ORIGIN OF SPECIES.

INTRODUCTION.

When on board II.M.S. * Beagle,' as naturalist, I was mucli stnick
with certain facts in the distribution of the organic beings inhabii
ing South America, and in the geological relations of the present to
the past inhabitants of that continent. These facts, as will be seen
in the latter chapters of this volume, seemed to throw some light
on the origin of species — that mystery of mysteries, as it has been
called by one of our greatest philosophers. On my return home, it
occurred to me, in 1837, that something might perhaps be made out
on this question by patiently accumulating and reflecting on all
BOx'-ts of facts which could possibly have any bearing on it. After
five years' work I allowed myself to speculate on the subject, and
drew up some short notes ; these I enlarged in 1844 into a sketch
of the conclusions, wbich then seemed to me probable : from that
period to the present day I have steadily pursued the same object.
I hope that I may be excused for entering on these personal details,
as I give them to show that I have not been hasty in coming to a
decision.

My work is now (1859) nearly fmished ; but as it will take me
many more years to complete it, and as my health .is far from-
strong, I have been urged to publish this Abstract. I have more
especially been induced to do this, as Mr. Wallace, who is now
studying the natural history of the Malay archipelago, has arrived
at almost exactly the same general conclusions that I have on the
origin of species. In 1858 he sent me a memoir on this subject,
with a request that I would forward it to Sir Charles Lyell, who
sent it to the Linnean Society, and it is published in the third
volume of the Journal of that Society. Sir C. Lyell and Dr. Hooker,
who both knew of my work — the latter having read my sketch of
1844 — honoured me by thinking it advisable to publish, with Mr.
Wallace's excellent memoir, some brief extracts from my manu-
scripts.

This Abstract^ which I now publish, must necessarily be im-
perfect. I cannot here give references and authorities for my

B

JMTRODUCTION.

several statements ; and I must trust to the reader reposing soms
confidence in my accuracy. ISId doubt errors will have crept in,
though I hope I have always been cautious in trusting to good
iuthorities alone. I can here give only the general conclusions at
which 1 have arrived, with a few facts in illustration, but which,
I hope, in most cases will suffice. No one can feel more sensible
i-han I do of the necessity of hereafter publishing in detail all the
facts, with references, on which my conclusions have been grounded ;
and I hope in a future work to do this. For I am well aware that
scarcely a single point is discussed in this volume on which facts
cannot be adduced, often apparently leading to conclusions directly
opposite to those at which I have arrived. A fair result can be
obtained only by fully stating and balancing the facts and argu-
ments on both sides of each question ; and this is here impossible.

I much regret that want of space prevents my having the satis-
faction of acknowledging the generous assistance which I have
received from very many naturalists, some of them personally un-
known to me. I cannot, however, let this opportunity pass without
expressing my deep obligations to Dr. Hooker, who, for the last
fifteen years, has aided me in every possible \vslj by his large stores
of knowledge and his excellent judgment.

In considering the Origin of Species, it is quite conceivable that
a naturalist, reflecting on the mutual affinities of organic beings,
on their embryological relations, their geographical distribution,
geological succession, and other such facts, might come to the con-
clusion that species had not been independently created, but had
descended, like varieties, from other species. Nevertheless, such a
conclusion, even if well founded, would be unsatisfactory, until it
could be shown how the innumerable species inhabiting this world
have been modified, so as to acquire that perfection of structure
and coadaptation which justly excites our admiration. Naturalists
continually refer to external conditions, such as climate, food, &c.,
as the only possible cause of variation. In one limited sense, as
we shall hereafter see, this may be true ; but it is preposterous to
attribute to mere external conditions, the structure, for instance, of
the woodpecker, with its feet, tail, beak, and tongue, so admirably
adapted to catch insects under the bark of trees. In the case of the
mistletoe, which draws its nourishment from certain trees, which
has seeds that must be transported by certain birds, and which has
flowers with separate sexes absolutely requiii^ig the agency of
certain insects to biing pollen from one flower to the other, it is
equally preposterous to account for the stricture of this parasite,
wllh its relations to several distinct organic beings, by the offecti?

INTRODUCTIOxN.

of external conditions, or of habit, or of the volition of the plant
itself.

It is, therefore, of the highest importance to gain a clear insight
into the means of modification and coadaptatiou. At the commence-
ment of my observations it seemed to me probable that a careful
Htudy of domesticated animals and of cultivated plants would offer
the best chance of making out this obscure problem. Nor have
I been disappointed ; in this and in all other perplexing cases I
have invariably found that our knowledge, imperfect though it be, ol
variation under domestication, afforded the best and safest clue. I
may venture to express my conviction of the high value of such
studies, although they have been very commonly neglected by
naturalists.

From these considerations, I shall devote the first chapter of this
Abstract to Variation under Domestication. AVe shall thus see that
a large amount of hereditary modification is at least possible ; and,
what is equally or more important, v/e shall see how great is the
power of man in accumulating by his Selection successive slight
variations. I will then pass on to the variability of species in a
state of nature ; but I shall, unfortunately, be compelled to treat
this subject far too briefly, as it can be treated properly only by
giving long catalogues of facts. We shall, however, be enabled to
discuss what circumstances are most favourable to variation. In
the next chapter the Struggle for Existence amongst all organic
beings throughout the world, which inevitably follows from the
high geometrical ratio of their increase, will be considered. This is
the doctrine of Malthus, applied to the whole animal and vegetable
kingdoms. As many more individuals of each species are born than
can possibly survive; and as, consequently, there is a frequently
recurring struggle for existence, it follows that any being, if it vary
however slightly in any manner profitable to itself, under the com-
plex and sometimes varying conditions of life, will have a better
chance of surviving, and thus be naturally selected. From the
strong principle of inheritance, any selected variety will tend to
propagate its new and modified form.

This fundamental subject of Natural Selection will be treated at
some length in the fourth chapter; and we shall then see how
Natural Selection almost inevitably causes much Extinction of the
less improved forms of life, and leads to what I have called Diver-
gence of Character. In the next chapter I shall discuss the complex
and little known laws of variation. In the five succeeding chapters,
the most apparent and gravest difficulties in accepting the theory
will be given : namely, first, the difficulties of trarsitions, or how a

B 2

IXTRODUCTinx.

simple being or a simple organ can be changed and perfected ink*
a highly developed being or into an elaborately constructed organ ;
secondly, the subject of Instinct, or the mental powers of animals ;
thirdly, Hybridism, or the infertility of species and the fertility of
varieties when intercrossed ; and fourthly, the imperfection of the
Geological Record. In the next chapter I shall consider the geo-
logical succession of organic beings throughout time ; in the twelfth
and thirteenth, their geographical distribution throughout space ; in
the fourteenth, their classification or mutual affinities, both when
mature and in an embryonic condition. In the last chapter I shall
give a brief recapitulation of the whole work, and a few concluding
remarks.

No one ought to feel surprise at much remaining as yet un-
explained in regard to the origin of species and varieties, if he make
due allowance for our profound ignorance in regard to the mutual
relations of the many beings which live around us. Who can ex-
plain why one species ranges widely and is very numerous, and
why another allied species has a narrow range and is rare ? Yet
these relations are of the highest importance, for they determine the
present welfare and, as I believe, the future success and modification
of every inhabitant of this world. Still less do we know of the
mutual relations of the innumerable inhabitants of the world during
the many past geological epochs in its history. Although much
remains obscure, and will long remain obscure, I can entertain no
doubt, after the most deliberate study and dispassionate judgment
of which I am capable, that the view which most naturalists until
recently entertained, and which I formerly entertained — namely,
that each species has been independently created — is erroneous.
I am fully convinced that species are not immutable ; but that
those belonging to what are called the same genera are lineal
descendants of some other and generally extinct species, in the
same manner as the acknowledged varieties of any one species are
the descendants of that species Furthermore, I am convinced
that Natural Selection has been the most important, but not the
exclusive, means of modificatioD.

CiiAP. I.] V^ARIATION UNDER DOMESTICATION.

CHAPTEK L

Vabiation under Domestication.

Causes of Variability — Effects of Habit and the use or disuse cf Parts —
Correlated Variation — Inheritance — Character of Domestic Varieties
— Difficulty of distinguishing between Varieties and Species — Origin
of Domestic Varieties from one or more Species — Domestic Pigeons_
their Differences and Origin — Principles of Selection, anciently fol-
lowed, their Effects — Methodical and Unconscious Selection — Un-
known Origin of our Domestic Productions — Circumstances favour-
able to Man's power of Selection.

Causes of Variahillty.

When we compare the individuals of the same variety or sub-
variety of our older cultivated plants and animals, one of the first
points which strikes us is, that they generally differ more from
each other than do the individuals of any one species or variety in
a state of nature. And if we reflect on the vast diversity of the
plants and animals which have been cultivated, and which have
varied during all ages under the most different climates and treat-
ment, we are driven to conclude that this great variability is due
to our domestic productions having been raised under conditions of
life not so uniform as, and somewhat different from, those to which
the parent-species had been exposed under nature. There is, also,
some probability in the view propounded by Andrew Knight, that
this variability may be partly connected with excess of food. It
seems clear that organic beings must be exposed during several
generations to new conditions to cause any great amount of varia-
tion ; and that, when the organisation has once begun to vary, it
generally continues varying for many generations. No case is on
record of a variable organism ceasing to vary under cultivation.
Our oldest cultivated plants, such as wheat, still yield new varie-
ties: our oldest domesticated animals are still capable of rapid
improvement or modification.

As far as I am able to judge, after long attending to the subject; i
the conditions of life appear to act in two ways, — directly on the/
whole organisation or on certain parts alone, and indirectly byl
aifecting the reproductiye system. With respect to the direct

6 VARIATION UNDER DOMESTICATION. [Cbap. I.

action, we must bear in mind that in every case, as Professoi
Weismann has lately insisted, and as I have incidentally shown in
niv work on ' Variation under Domestication,' there are two
factors : namely, the nature of the organism, and the nature of the
conditions. The former seems to be much the more important •
for nearly similar variations sometimes arise under, as far as wf
can judge, dissimilar conditions ; and, on the other hand, dissimilar
variations arise under conditions which appear to be nearly uniform.
The effects on the offspring are either definite or indefinite. They
may be considered as definite when all or nearly all the offspring of
individuals exposed to certain conditions during several generations
aro modified in the same manner. It is extremely difiicult to come
to any conclusion in regard to the extent of the changes which have
been thus definitely induced. There can, however, be little doubt
about many slight changes, — such as size from the amount of food, ^
colour from the nature of the food, thickness of the skin and hair
fi'om climate, &c. Each of the endless variations which we see in
the plumage of our fowls must have had some efficient cause ; and |
if the' same cause were to act uniformly during a long series of '
generations on many individuals, all probably would be modified in
the same manner. Such facts as the complex and extraordinary
out-growths which invariably follow from the insertion of a minute
drop of poison by a gall-producing insect, show us what singular
modifications might result in the case of plants from a chemical
change in the nature of the sap.

Indefinite variability is a much more common result of changed
conditions than definite variability, and has probably played a more
important part in the formation of our domestic races. We see
indefinite variability in the endless slight peculiarities which dis-
tinguish the individuals of the same species, and which cannot be
accounted for by inheritance from either parent or from some more
remote ancestor. Even strongly-marked differences occasionally
appear in the young of the same litter, and in seedlings from the
same seed-capsule. At long intervals of time, o-ut of millions ol
individuals reared in the same country and fed on nearly the samo
food, deviations of structure so strongly pronounced as to deserve
to be called monstrosities arise ; but monstrosities cannot be
separated by any distinct line from slighter variations. All such
changes of structure, whether extremely slight or strongly marked,
which appear amongst many individuals living together, may be
considered as the indefinite effects of the conditions of life on each
individual organism, in nearly the same manner as a chill aflfecTs
different men in an indefinite manner, according to their stato

CHAr. I.] VARIATION UNDER DOMESTICATION.

of body or constitution, causing coughs or colds, rheumatism, or
inflammations of various organs.

With respect to what I have called the indirect action of changed
conditions, namely, through the reproductive system being affected,
WQ may infer that variability is thus induced, partly from the fact
of this system being extremely sensitive to any change in the con-
ditions, and partly from the similarity, as Kolreuter and others
have remarked, between the variability which follows from the
crossing of distinct species, and that which may be observed with
plants and animals when reared under new or unnatural conditions.
Many facts clearly show how eminently susceptible the reproduc-
tive system is to very slight changes in the surrounding conditions.
Nothing is more easy than to tame an animal, and few things more
difficult than to get it to breed freely under confinement, even when
the male and female unite. How many animals there are which
will not breed, though kept in an almost free state in their native
country ! This is generally, but erroneously, attributed to vitiated
instincts. Many cultivated plants display the utmost vigour, and
yet rarely or never seed ! In some few cases it has been discovered
that a very trifling change, such as a little more or less water at
some particular period of growth, will determine whether or not a
plant will produce seeds. I cannot here give the details which
I have collected and elsewhere published on this curious subject ;
but to show how singular the laws are which determine the repro-
duction of animals under confinement, I may mention that car-
nivorous animals, even from the tropics, breed in this country
pretty freely under confinement, with the exception of the planti-
grades or bear family, which seldom produce j^oung ; whereaa
carnivorous birds, with the rarest exceptions, hardly ever lay fertile
eggs. Many exotic plants have pollen utterly worthless, in the
same condition as in the most sterile hybrids. When, on the one
hand, we see domesticated animals and plants, though often weak
and sickly, breeding freely under confinement ; and when, on the
other hand, we see individuals, though taken young from a state of
nature joerfectly tamed, long-lived and healthy (of which I could
give numerous instances), yet having their reproductive system so
seriously affected by unperceived causes as to fail to act, we need
not be surprised at this system, when it does act under confinement,
acting irregularly, and producing offspring somewhat unlike their
parents. I may add, that as some organisms breed freely under
the most unnatural conditions (for instance, rabbits and ferrets kept
in hutches), showing that their reproductive organs are not easily
affected ; so will some animals and plants withstand domestication

VARIATION UNDER uuMESTICATION. [Chap, l.

or cultivation, and vary very slightly — perhaps hardly more than in
a state of nature.

Some naturalists have maintained that all variations are con-
nected with the act of sexual reproduction ; but this is certainly
an error ; for I have given in another work a long list of " sporting
plants," as they are called by gardeners ; — tliat is, of plants which
have suddenly produced a single bud with a new and sometimes
widely different character from that of the other buds on the same
plant. These bud variations, as they may be named, can be pro-
pagated by grafts, offsets, &c., and sometimes by seed. They occur
rarely under nature, but are far from rare under culture. As a
single bud out of the many thousands, produced year after year on
the same tree under uniform conditions, has been known suddenly
to assume a new character ; and as buds on distinct trees, growing
under different conditions, have sometimes yielded nearly the same
variety — for instance, buds on peach-trees producing nectarines,
and buds on common roses producing moss-roses — we clearly see
that the nature of the conditions is of subordinate importance in
comparison with the nature of the organism in determining each
particular form of variation ; — perhaps of not more importance than
the nature of the spark, by which a mass of combustible matter is
ignited, has in determining the nature of the flames.

Effects of Habit and of the Use or Disuse of Farts; Coir elated
Variation ; Inheritance,

Changed habits produce an inherited effect, as in the period of the
flowering of plants when transported fr©m one climate to another.
With animals the increased use or disuse of parts has had a more
marked influence ; thus I find in the domestic duck that the bones
of the wing weigh less nnd the bones of the leg more, in proportion
to the whole skeleton, than do the same bones in the wild-duck ;
and this change may be safely attributed to the domestic duck
flying much less, and walking more, than its wild parents. The
great and inherited development of the udders in cows and goats in
countries where they are habitually milked, in comparison with
these organs in other countries, is probably another instance of the
effects of use. Not one of our domestic animals can be named
which has not in some country drooping ears ; and the view which
has been suggested that the drooping is due to the disuse of the
muscles of the ear, from the animals being seldom much alarmed,
seems probable.

Many laws regulate variation, some few of which can be dimly

Chap. I.] VARIATION UNDER DOMESTICATION. 9

seen, and will hereafter be briefly discussed. I will here only
allude to what may be called correlated variation. Important
changes in the embryo or larva will probably entail changes in the
mature animal. In monstrosities, the correlations between quite
distinct parts are very curious ; and many instances are given in
Isidore GeotTroy St. Ililaire's great work on this subject. Breeders
believe that long limbs are almost always accompanied by an
elongated head. Some instances of correlation are quite whimsical :
thus cats which are entirely white and have blue eyes are generally
deaf; but it has been lately stated by Mr. Tait that this is confined
to the males. Colour and constitutional peculiarities go together,
of which many remarkable cases could be given amongst animals
and plants. From facts collected by Heusinger, it appears that
white sheep and pigs are injured by certain plants, whilst dark-
coloured individuals escape: Professor Wyman has recently com-
municated to me a good illustration of this fact ; on asking some
farmers in Virginia how it was that all their pigs were black, they
informed him that the pigs ate the paint-root (Lachnanthes),
which coloured their bones pink, and which caused the hoofs of all
but the black varieties to drop off; and one of the "crackers"
(i. e. Virginia squatters) added, '* we select the black members of a
litter for raising, as they alone have a good chance of living," Hair-
less dogs have imperfect teeth : long-haired and coarse-hairei
animals are apt to have, as is asserted, long or many horns ; pigeons
with feathered feet have skin between their outer toes ; pigeons
with short beaks have small feet, and those with long beaks large
feet. Hence if man goes on selecting, and thus augmenting, any
pecuUarity, he will almost certainly modify unintentionally other
parts of the structure, owing to the mysterious laws of correlation.

The results of the various, unknown, or but dimly understood
laws of variation are infinitely complex and diversified. It is weD
worth while carefully to study the several treatises on some of
our old cultivated plants, as on the hyacinth, potato, even the
dahlia, &c. ; and it is really surprising to note the endless points of
structure and constitution in which the varieties and sub-varieties
difier slightly from each other. The whole organisation seems to
have become plastic, and departs in a slight degree from that of the
parental type.

Any variation which is not inherited is unimportant for us.
But the number and diversity of inheritable deviations of structure,
both those of slight and those of considerable physiological impor-
tance, are endless. Dr. Prosper Lucas's treatise, in two large
TOlumes, is the fullest and the best on this subject. No breed ei

10 VARIATION UNDER DOMESTICATION. [Chap. I

doubts how strong is the tendency to inheritance ; that like pro*
duces like is his fundamental belief: doubts have been thrown oa
this principle only by theoretical writers. When any deviation ol
structure often appears, and we see it in the father and child, we
cannot tell whether it may not be due to the same cause having
acted on both ; but when amongst individuals, apparently exposed
to the same conditions, any very rare deviation, due to some
extraordinary combination of circumstances, appears in the parent
— say, once amongst several million individuals — and it reappears
in the child, the mere doctrine of chances almost compels us to
attribute its reappearance to inheritance. Every one must have
heard of cases of albinism, prickly skin, hairy bodies, &c., appearing
in several members of the same family. If strange and rare
deviations of structure are really inherited, less strange and com-
moner deviations may be freely admitted to be inheritable.
Perhaps the correct way of viewing the whole subject would be, to
look at the inheritance of every character whatever as the rule, and
non-inheritance as the anomaly.

The laws governing inheritance are for the most part unknown.
No one can say why the same peculiarity in different individuals
of the same species, or in different species, is sometimes inherited
and sometimes not so ; why the child often reverts in certain
characters to its grandfather or grandmother or more remote ances-
tor ; why a peculiarity is often transmitted from one sex to both
sexes, or to one sex alone, more commonly but not exclusively to
the like sex. It is a fact of some importance to us, that peculiarities
appearing in the males of our domestic breeds are often transmitted,
either exclusively or in a much greater degree, to the males alone.
A much more important rule, which I think may be trusted, is
that, at whatever period of life a peculiarity first appears, it tends
to re-appear in the offspring at a corresponding age, though some-
times earlier. In many cases this could not be otherwise ; thus
the inherited peculiarities in the horns of cattle could appear only
in the offspring when nearly mature ; peculiarities in the silk-
worm are known to appear at the corresponding caterpillar or
cocoon stage. But hereditary diseases and some other facts make
me believe that the rule has a wider extension, and that, when
there is no apparent reason why a peculiarity should appear at
any particular age, yet that it does tend to appear in the offspring
at the same period at which it first appeared in the parent. I
believe this rule to be of the highest importance in explaining the
laws of embryology. These remarks are of course confined to the
first appearance of the peculiarity, and not to the primary cause

Chap. 1.] VAKIATION UNDER r-OMESTICATlON. H

which may have acted on the ovules or on the male element ; in
nearly the same manner as the increased length of the hoins in the
cffspring from a short-horned cow by a long-horned bull, though
appearing late in life, is clearly due to the male element. -

Having alluded to the subject of reversion, I may here refer to a
statement often made by naturalists — namely, that our domestic
varieties, when run wild, gradually but invariably revert in charac-
tor to their aboriginal stocks. Hence it has been argued that no
deductions can be drawn from domestic races to species in a state of
nature. I have in vain endeavoured to discover on what decisive
facts the above statement has so often and so boldly been made.
There would be great difficulty in proving its truth : we may safely
conclude that very many of the most strongly marked domestic varie-
ties could not possibly live in a wild state. In many cases we do not
know what the aboriginal stock was, and so could not tell whether
or not nearly perfect reversion had ensued. It would be necessary,
in order to prevent the effects of intercrossing, that only a single
variety should have been turned loose in its new home. Neverthe-
less, as our varieties certainly do occasionally revert in some of
their characters to ancestral forms, it seems to me not improbable
that if we could succeed in naturalising, or were to cultivate,
during many generations, the several races, for instance, of the
cabbage, in very poor soil (in which case, however, some effect
would have to be attributed to the definite action of the poor soil),
that they would, to a large extent, or even wholly, revert to the
wild aboriginal stock. Whether or not the experiment would
succeed, is not of great importance for our line of argument ; for by
the experiment itself the conditions of life are changed. If it could
be shown that our domestic varieties manifested a strong tendency
to reversion, — that is, to lose their acquired characters, whilst kept
under the same conditions, and whilst kept in a considerable body,
so that free intercrossing might check, by blending together, any
slight deviations in their structure, in such case, I grant that we
could deduce nothing from domestic varieties in regard to species.
But there is not a shadow of evidence in favour of this view : to
assert that we could not breed our cart and race-horses, long and
Rhort-horned cattle, and poultry of various breeds, and esculent
vegetables, for an unlimited number of generations, would be
opposed to all experience.

12 CHARACTER OF DOMESTIC VARIETIES. [Cha?. I.

Character of Domestic Varieties: difficulty of distinguishing
between Varieties and Species; origin of Domestic Varieties\
from one or more Species. !

When we look to the hereditary varieties or races of our domestic
animals and plants, and compare them with closely allied species,
we generally perceive in each domestic race, as already remarked, 1
less uniformity of character than in true species. Domestic races '
often have a somewhat monstrous character ; by which I mean,
that, although differing from each other, and from other species of
the same genus, in several trifling respects, they often differ in an
extreme degree in some one part, both when compared one with
another, and more especially when compared with the species under
nature to which they are nearest allied. With these exceptions
(and with that of the perfect fertility of varieties when crossed, — a
subject hereafter to be discussed), domestic races of the same species
differ from each other in the same manner as do the closely-allied
species of the same genus in a state of nature, but the differences
in most cases are less in degree. This must be admitted as true,
for the domestic races of many animals and plants have beec
ranked by some competent judges as the descendants of aborigi-
nally distinct species, and by other competent judges as mere
varieties. If any well marked distinction existed between a
domestic race and a species, this source of doubt would not so
perpetually recur. It has often been stated that domebtic races
do not differ from each other in characters of generic value. It can
be shown that this statement is not correct ; but naturalists differ
much in determining what characters are of generic value ; all
such valuations being at present empirical. When it is explained
now genera originate under nature, it will be seen that we have
no right to expect often to find a generic amount of difference
in our domesticated races.

In attempting to estimate the amount of structural difference
between allied dom.estic races, we are soon involved in doubt,
from not knowing whether they are descended from one or several
parent species. This point, if it could be cleared up, would be
interesting ; if, for instance, it could be shown that the greyhound,
bloodhou.nd, terrier, spaniel, and bull-dog, which we all know
propagate their kind truly, were the offspring of any single species,
then such facts would have great weight in making us doubt about
the immutability of the many closely allied natural species — for
instance, of the many foxes — inhabiting different quarters of the
world. 1 do not believe, as we shall presently see, that the whole

C!f AP. L] CHARACTER OF DOMESTIC VARIETIES. 13

amount of difference between the several breeds of the do^ has bee??
produced under domestication ; I believe that a small part of the
difference is due to tlieir being descended from distinct species. la
the case of strongly marked races of some other domesticated
species, there is presumptive or even strong evidence, that all are
descended from a single wild stock.

It has often been assumed that man has chosen for domestica-
tion animals and plants having an extraordinary inherent tendency
to vary, and likewise to withstand diverse climates I do not dispute
that these capacities have added largely to the value of most of our
domesticated productions ; but how could a savage possibly know,
when he first tamed an animal, whether it would vary in succeeding
generations, and whether it would endure other climates ? Has
the little variability of the ass and goose, or the small power of
endurance of warmth by the reindeer, or of cold by the common
camel, prevented their domestication? I cannot doubt that if
other animals and plants, equal in number to our domesticated
productions, and belonging to equally diverse classes and countries,
were taken from a state of nature, and could be made to breed for
an equal number of generations under domestication, they would
on an average vary as largely as the parent species of our existing
domesticated productions have varied.

In the case of most of our anciently domesticated animals and
plants, it is not possible to come to any definite conclusion, whether
they are descended fKom one or several wild species. The argument
mainly relied on by those who believe in the multiple origin of our
domestic animals is, that we find, in the most ancient times, on the
monuments of Egypt, and in the lake-habitations of Switzerland,
much diversity in the breeds; and that some of the?e ancient
breeds closely resemble, or are even identical with, those still exist-
ing. But this only throws far backwards the history of civilisation,
and shows that animals were domesticated at a much earlier period
than has hitherto been supposed. The lake-inhabitants of Swit-
zerland cultivated several kinds of wheat and barley, the pea, the
poppy for oil, and flax; and they possessed several domesticated
animals. They also carried on commerce with other nations. All
this clearly shows, as Heer has remarked, that they had at this
early age progressed considerably in civilisation ; and this again
implies a long continued previous period of less advanced civilisation,
during which the domesticated animals, kept by different tribes in
different districts, might have varied and given rise to distinct races.
Since the discovery of flint tools in the superficial formations ol
many parts of the world, all geologists believe that barbarian man

14 CHARACTER OF DOMESTIC VARIETIES. [Chap.1.

existed at an enormously remote period ; and we know that at the
present day there is hardly a tribe so barbarous, as not to have
domesticated at least the dog.
f> The origin of most of our domestic animals will probably for
ever remain vague. But I may here state, that, looking to the
domestic dogs of the whole world, I have, after a laborious collection
of all known facts, come to the conclusion that several wild species
of Canidee have been tamed, and that their blood, in some cases
mingled together, flows in the veins of our domestic breeds. In
regard to sheep and goats I can form no decided opinion. From
facts communicated to me by Mr. Blyth, on the habits, voice, con-
stitution, and structure of the humped Indian cattle, it is almos;
certain that they are descended from a different aboriginal stock
from our European cattle ; and some competent judges believe that
these latter have had two or three wild progenitors, — whether or not
these desei ve to be called species. This conclusion, as well as that
of the specific distinction between the humped and common cattle,
may, indeed, be looked upon as established by the admirable re-
searches of Professor RUtimeyer. With respect to horses, from
reasons which I cannot here give, I am doubtfully inclined to believe,
in opposition to several authors, that all the races belong to the same
species. Having kept nearly all the English breeds of the fowl
alive, having bred and crossed them, and examined their skeletons,
it appears to me almost certain that all are the descendants of the
wild Indian fowl, Gallus bankiva ; and this is the conclusion of
Mr. Blyth, and of others who have studied this bird in India. In
regard to ducks and rabbits, some breeds of which differ much from
each other, the evidence is clear that they are all descended
from the common wild duck and rabbit.

The doctrine of the origin of our several domestic races fron.
several aboriginal stocks, has been carried to an absurd extreme bj
some authors. They believe that every race which breeds true, lej
the distinctive characters be ever so slight, has had its wild proto-
type. At this rate there must have existed at least a score of
species of wild cattle, as many sheep, and several goats, in Europe
alone, and several even within Great Britain. One author believes
that there formerly existed eleven wild species of sheep peculiar to
Great Britain ! When we bear in mind that Britain has now not
one peculiar mammal, and France but few distinct from those of
Germany, and so with Hungary, Spain, &c., but that each of these
kingdoms possesses several peculiar breeds of cattle, sheep, &c., we
must admit that many domestic breeds must have originated in
Europe ; f )r wh«3nce otherwise could they have been derived ? So it is

y

Chap. L] DOMESTH: PIGEONS. 18

ia India. Even in the case of the breeds of the domestic dog through-
out the world, which I admit are descended from several wild spe-
cies, it cannot be doubted that there has been an immense amount
of inherited variation ; for who will believe that animals closely
resembling the Italian greyhound, the bloodhound, the bull-dog,
pug-dog, or Blenheim spaniel, &c. — so unlike all wild Canidte —
ever existed in a state of nature ? It has often been loosely said
that all our races of dogs have been produced by the crossing of a
few aboriginal species ; but by crossing we can only get forms in
some degree intermediate between their parents ; and if we account
for our several domestic races by this process, we must admit the
former existence of the most extreme forms, as the Italian grey-
hound, bloodhound, bull-dog, &c., in the wild state. Moreover,
the possibility of making distinct races by crossing has been greatly
exaggerated. Many cases are on record, showing that a race may
be modified by occasional crosses, if aided by the careful selection
of the individuals which present the desired character; but to
obtain a race intermediate between two quite distinct races, would
be very difficult. Sir J. Sebright expressly experimented with this
object, and failed. 1'he offspring from the first cross between two
pure breeds is tolerably and sometimes (as I have found with
pigeons) quite uniform in character, and everything seems simple
enough ; but when these mongrels are crossed one with another for
several generations, hardly two of them are alike, and then the
difficulty of the task becomes manifest.

Breeds of tJte Domestic Pigeon, their Differences and Origin.

Believing that it is always best to study some special group, I
have, after deliberation, taken up domestic pigeons. I have kept
every breed which I could purchase or obtain, and have been most
kindly favoured with skins from several quarters of the world, more
especially by the Hon. W. Elliot from India, and by the Hon. C.
Murray from Persia. Many treatises in different languages have
been published on pigeons, and some of them are very important,
as being of considerable antiquity. I have associated with several
eminent fanciers, and have been permitted to join two of the London
Pigeon Clubs. The diversity of the breeds is something astonishing.
Compare the English carrier and the short-faced tumbler, and see
the wonderful difference in their beaks, entailing corresponding
differences in their skulls. The carrier, more especially the male
bird, is also remarkable from the wonderful development of the
caninculated skin about the head ; and this is accompanied by
greatly elongated eyelids, very large external orifices to the' nostrila,

36 DOMESTIC riGEOXS. [Chap. L

and a wide gape of mouth. The short-faced tumbler has a beak in
outline ahnost like that of a finch; and the common tumbler has
the singular inherited habit of flying at a great height in a compact
flock, and tumbling in the air head over heels. The runt is a bird
of great size, with long massive beak and large feet ; some of the
sub-breeds of runts have very long necks, others very long wings
and tails, others singularly short tails. The barb is allied to the
carrier, but, instead of a long beak, has a very short and broad one.
The pouter has a much elongated body, wings, and legs ; and its
enormously developed crop, which it glories in inflating, may well
excite astonishment and even laughter. The turbit has a short and
conical beak, with a line of reversed feathers down the breast ; and
it has the habit of continually expanding, slightly, the upper part of
the oesophagus. The Jacobin has the feathers so much reversed
along the back of the neck that they form a hood ; and it has, pro-
portionally to its size, elongated wing and tail feathers. The
trumpeter and laugher, as their names express, utter a very difl'erent
coo from the other breeds. The fantail has thirty or even forty
tail-feathers, instead of twelve or fourteen — the normal number in
all the members of the great pigeon family : these feathers are kept
expanded, and are carried so erect, that in good birds the head and
tail touch: the oil-gland is quite aborted. Several other less
distinct breeds might be specified.

In the skeletons of the several breeds, the development of the
bones of the face in length and breadth and curvature differs enor-
mously. The shape, as well as the breadth and length of the ramus
of the lower jaw, varies in a highly remarkable manner. The
caudal and sacral vertebra3 vary in number ; as does the number of
ihe ribs, together with their relative breadth and the presence of
processes. The size and shape of the apertures in the sternum are
highly variable ; so is the degree of divergence and relative size of
the two arms of the furcula. The proportional width of the gape
of mouth, the proportional length of the eyelids, of the orifice of
the nostrils, of the tongue (not always in strict correlation with the
length of beak), the size of the crop and of the upper part of the
oesophagus ; the development and abortion of the oil-gland ; the
number of the primary wing and caudal feathers ; the relative
length of the wing and tail to each other and to the body ; the
relative length of the leg and foot ; the number of scutellaj on
the toes, the development of skin between the toes, are all points
of structure which are variable. The period at which the perfect
plumage is acquired varies, as does the state of the down with wliich
the nestling birds are clothed when hatched. The shape and size

Chap. LI DOMESTIC PIGEONS. 17

3f the eggs vary. The manner of flight, and in some breeds the
Toice and disposition, differ remarkably. Lastly, in certain breeds,
the males and females have come to differ in a slight degree from
each other.

Altogether at least a score of pigeons might be chosen, which, if
bhown to an ornithologist, and he were told that they were wild
birds, would certainly be ranked by him as well-defined species.
Moreover, I do not believe that any ornithologist would in this
case place the English carrier, the short-faced tumbler, the runt^ the
barb, pouter, and fantail in the same genus ; more especially as in
each of these breeds several truly-inherited sub-breeds, or species, as
he would call them, could be shown him.

Great as are the differences between the breeds of the pigeon,
I am fully convinced that the common opinion of naturalists is
correct, namely, that all are descended from the rock-pigeon
(Columba livia), including under this term several geographical
races or sub-species, which differ from each other in the most trifling
respects. As several of the reasons which have led me to this
belief are in some degree applicable in other case?, I will here briefly
give them. If the several breeds are not varieties, and have not
proceeded from the rock-pigeon, they must have descended from at
least seven or eight aboriginal stocks ; for it is impossible to make
the present domestic breeds by the crossing of any lesser number :
how, for instance, could a pouter be produced by crossing two
breeds unless one of the parent-stocks possessed the characteristic
enormous crop? The supposed aboriginal stocks must all have
been rock-pigeons, that is, they did not breed or willingly perch on
trees. But besides C. livia, with its geographical sub-species, only
two or three other species of rock-pigeons are known ; and these
have not any of the characters of the domestic breeds. Hence the
supposed aboriginal stocks must either still exist in the countries
where they were originally domesticated, and yet be unknown to
ornithologists ; and this, considering their size, habits, and remark-
able characters, seems improbable ; or they must have become
extinct in the wild state. But birds breeding on precipices, and
good fliers, are unlikely to be exterminated ; and the common rock-
pigeon, which has the same habits with the domestic breeds, has
not been exterminated even on several of the smaller British islets,
or on the shores of the Mediterranean. Hence the supposed exter-
mination of so many species having similar habits with the rock-
pigeon seems a very rash assumption. Morever, the several above-
named domesticated breeds have been transported to all parts of the
world, and, therefore, some of them must have been carried back

c

H^

18 DO.MESTIC PIGE0N3. [CiL^. 1.

again into their native country ; but not one has become wild or
feral, though the dovecot-pigeon, which is the rock-pigeon in a very
slightly altered state, has become feral in several places. Again,
all recent experience shows that it is difficult to get wild animals to
breed freely under domestication; yet, on the hypothesis of thr
multiple origin of our pigeons, it must be assumed that at least
f^Y&i or eight species were so thoroughly domesticated in ancient
times by half-civilised man, as to be quite prolific under con-
finement.

An argument of great weight, and applicable in several other
eases, is, that the above-specified breeds, though agreeing generally
with the wild rock-pigeon in constitution, habits, voice, colouring,
and in most parts of their structure, yet are certainly highly abnor-
mal in other parts ; we may look in vain through the whole great
family of Columbida3 for a beak like that of the English carrier, or
that of the short-faced tumbler, or barb ; for reversed feathers like
those of the Jacobin ; for a crop like that of the pouter ; for tail-
feathers like those of the fantail. Hence it must be assumed not
only that half-civilised man succeeded in thoroughly domesticating
several species, but that he intentionally or by chance picked out
extraordinarily abnormal species; and further, that these very
species have since all become extinct or unknown. So many strange
contingencies are improbable in the highest degree.

Some facts in regard to the colouring of pigeons well deserve
consideration. The rock-pigeon is of a slaty-blue, with white loins;
but the Indian sub-species, 0. intermedia of Strickland, has this
part bluish. The tail has a terminal dark bar, with the outer
feathers externally edged at the base with white. The wings have
two black bars. Some semi- domestic breeds, and some truly wild
breeds, have, besides the two black bars, the wings chequered with
black. These several marks do not occur together in any other
species of the whole family. Now, in every one of the domestic
breeds, taking thoroughly well-bred birds, all the above marks, even
to the white edging of the outer tail-feathers, sometimes concur
perfectly developed. Moreover, when birds belonging to two or
more distinct breeds are crossed, none of which are blue or have
any of the above-specified marks, the mongrel ofi'spring are very
apt suddenly to acquire these characters, l^o give one instance out of
several which I have observed : — I crossed some white fantails, which
breed very true, with some black barbs — and it so happens that
blue varieties of barbs are so rare that I never heard of an instance
in England ; and the mongrels were black, brown, and mottled. I
also crossed a barb with a spot, which is a white bird with a rod

Chap. I.J DOMESTIC PIGEONS. 19

tail and red spot on the farehead, and which notoriously breeds very
true ; the mongrels were dusky and mottled. 1 then crossed one of
the mongrel barb-fantails with a mongrel barb-spot, and they pro-
duced a bird of as beautiful a blue colour, with the white loins,
double black wiug-bar, and barred and white-edged tail- feathers, as
any wild rock-pigeon ! We can understand these facts, on the
well-known principle of reversion to ancestral characters, if all
the domestic breeds are descended from the rock-pigeon. But if
we deny this, we must make one of the two following highly im-
probable suppositions. Either, first, that all the several imagined
aboriginal stocks were coloured and marked like the rock-pigeon,
although no other existing species is thus coloured and marked, so
that in each separate breed there might be a tendency to revert to
the very same colours and markings. Or, secondly, that each
breed, even the purest, has within a dozen, or at most within a
score, of generations, been crossed by the rock-pigeon : 1 say within
a dozen or twenty generations, for no instance is known of crossed
descendants reverting to an ancestor of foreign blood, removed by a
greater number of generations. In a breed which has been crossed
only once, the tendency to revert to any character derived from
such a cross will naturally become less and less, as in each succeed-
ing generation there will be less of the foreign blood ; but when
there has been no cross, and there is a tendency in the breed to
revert to a character which was lost during some former generation,
this tendency, for all that we can see to the contrary, may be
transmitted undiminished for an indefinite number of generations.
These two distinct cases of reversion are often confounded together
by those who have written on inheritance.

Lastly, the hybrids or mongrels from between all the breeds of
. the pigeon are perfectly fertile, as I can state from my own obser-
vations, purposely made, on the most distinct breeds. Now, hardly
any cases have been ascertained with certainty of hybrids from two
quite distinct species of animals being perfectly fertile. Some
authors believe that long-continued domestication eliminates this
strong tendency to sterility in species. From the history of the
dog, and of some other domestic animals, this conclusion is pro-
bably quite correct, if applied to species closely related to each
other. But to extend it so far as to suppose that species, aborigi-
. naUy as distinct as carriers, tumblers, pouters, and fantails now arCs
should yield offspring perfectly fertile inter se, would be rash in the
extreme.

From these several reasons, namely, — the improbability of man
haying formerly made seven or eight supposed species of pigeons tc

c 2

20 DOMESTIC PIGEONS. [Ouap. 1.

breed freely under domestication; — these supposed species "being
quite unknown in a wild state, and their not having become any-
where feral ; — these species presenting certain very abnormal cha-
racters, as compared with all other Columbidse, though so like the
rock-pigeon in most respects ; — the occasional re-appearance of
the blue colour and various black marks in all the breeds, both
when kept pure and when crossed ; — and lastly, the mongrel off-
spring being perfectly fertile; — from these several reasons, taken
together, we may safely conclude that all our domestic breeds are
descended from the rock-pigeon or Columba livia with its geogra-
Iphical s*ub-species.

In favour of this view, I may add, firstly, that the wild C. livia
has been found capable of domestication in Europe and in India;
and that it agrees in habits and in a great number of points of struc-
ture with all the domestic breeds. Secondly, that, although an
English carrier or a short-faced tumbler differs immensely in certain
characters from the rock-pigeon, yet that, hj comparing the several
sub-breeds of these two races, more especially those brought from
distant countries, we can make, between them and the rock-pigeon,
an almost perfect series ; so we can in some other cases, but not
with all the breeds. Thirdly, those characters whicli are mainly dis-
tinctive of each breed are in each eminently variable, for instance
the wattle and length of beak of the carrier, the shortness of that
of the tumbler, and the number of tail-feathers in the fantail ; and
the explanation of this fact will be obvious when we treat of Selec-
tion. Fourthly, pigeons have been watched and tended with the
utmost care, and loved by many people. They have been domesti-
cated for thousands of years in several quarters of the world ; the
eorliest known record of pigeons is in the fifth ^Egyptian dynasty,
about 3000 b.c, as was pointed out to me by Professor Lepsius ;
but Mr. Birch informs me that pigeons are given in a bill of fare in
the previous dynasty. In the time of the Komans, as we hear from
Pliny, immense prices were given for pigeons ; " nay, they are come
to this pass, that they can reckon up their pedigree and race."
Pigeons were much valued by Akber Khan in India, about the year
1600 ; never less than 20,000 pigeons were taken with the court.
" The monarchs of Iran and Turan sent him some very rare birds ; **
and, continues the courtly historian, " His Majesty by crossing the
breeds, which method was never practised before, has improved them
astonishingly." About this same period the Dutch were as eager
about pigeons as were the old Romans. The paramount importance
of these considerations in explaining the immense amount of vari-
ation which pigeons have undergone, will likewise be obvious when

Chap. I.] DOMESTIC PIGEONS. 21

WB treat of Selection. We shall then, also, see how it is that tho
several breeds so often have a somewhat monstrous character. It
is also a most favourable circumstance for the production of dis-
tinct breeds, that male and female pigeons can be easily mated for
life; and thus different breeds can be kept together in the same
aviary. '^

I have discussed the probable origin of domestic pigeons at some,
yet quite insufficient, length ; because when I first kept pigeons
and watched the several kinds, well knowing how truly they breed,
I felt fully as much difficulty in believing that since they had been
domesticated they had all proceeded from a common parent, as any
naturalist could in coming to a similar conclusion in regard to the
many species of finches, or other groups of birds, in nature. One
circumstance has struck me much ; namely, that nearly all the
breeders of the various domestic animals and the cultivators of
plants, with whom I have conversed, or whose treatises I have read,
are firmly convinced that the several breeds to which each has at-
tended, are descended from so many aboriginally distinct species.
Ask, as I have asked, a celebrated raiser of Hereford cattle, whether
his cattle might not have descended from Long-horns, or both from
a common parent-stock, and he will laugh you to scorn. 1 have
never met a pigeon, or poultry, or duck, or rabbit fancier, who was
not fully convinced that each main breed was descended from a dis-
tinct species. Van Mens, in his treatise on pears and apples, shows
how utterly he disbelieves that the several sorts, for instance a
Kibston-pippin or Codlin-apple, could ever have proceeded from the
seeds of the same tree. Innumerable other examples could be given.
The explanation, I think, is simple: from long-continued study
they are strongly impressed with the differences between the several
races ; and though they well know that each race varies slightly,
for they win their prizes by selecting such slight differences, yet
they ignore all general arguments, and refuse to sum up in their
minds slight differences accumulated during many successive gene-
rations. May not those naturalists who, knowing far less of the
laws of inheritance than does the breeder, and knowing no more
than he does of the intermediate links in the long lines of descent,
yet admit that many of our domestic races are descended from the
same parents — may they not learn a lesson of caution, when they
deride the idea of species in a state of nature being lineal descendants
of other species ?

22 SELECTION BY MAN. [Chap. I

Frincijyles of Selection anciently folloived, and their Effects.

Let us now briefly consider the steps by which domestic races
have been produced, either from one or from several allied species.
Some effect may be attributed to the direct and definite action of
the external conditions of life, and some to habit; but he would bo
a bold man who would account by such agencies for the differences
between a dray and race horse, a greyhound and bloodhound, a car-
rier and tumbler pigeon. One of the most remarkable features in
our domesticated races is that we see in them adaptation, not indeed
to the animal's or plant's own good, but to man's use or fancy,
Some variations useful to him have probably arisen suddenly, or by
one step ; many botanists, for instance, believe that the fuller's teasel,
with its hooks, which cannot be rivalled by any mechanical con-
trivance, is only a variety of the wild Dipsacus ; and this amount
of change may have suddenly arisen in a seedling. So it has pro-
bably been with the turnspit dog ; and this is known to have been
the case with the ancon sheep. But when we compare the dray-
horse and race-horse, the dromedary and camel, the various breeds
of sheep fitted either for cultivated land or mountain pasture, with
the wool of one breed good for one purpose, and that of another
breed for another purpose ; when we compare the many breeds of
dogs, each good for man in different ways ; when we compare the
game-cock, so pertinacious in battle, with other breeds so little quar-
i-elsome, with "everlasting layers" which never desire to sit, and
with the bantam so small and elegant ; when we compare the host
of agricultural, culinary, orchard, and flower-garden races of plants,
most useful to man at different seasons and for different purposes, or so
beautiful in his eyes, we must, I think, look further than to mere
variability. We cannot suppose that all the breeds were suddenly
produced as perfect and as useful as we now see them ; indeed, in
many cases, we know that this has not been their history. The
key is man's power of accumulative selection : nature gives succes-
sive variations ; man adds them up in certain directions useful to
him. In this sense he may be said to have made for himself useful
^breeds.

The great power of this principle of selection is not hypothetical.
It is certain that several of our eminent breeders have, even within
a single lifetime, modified to a large extent their breeds of cattle and
sheep. In order fully to realise what they have done, it is almost
necessary to read several of the many treatises devoted to this sub-
ject, and to inspect the animals. Bleeders habitually speak of an
animal's organisation as something plastic, which they can mode?

Chaf. l] selection by man. 23

aliQOflt as they please. If I had space I could quote numerous x>a8-
sagcs to this effect from highly competent authorities. Youatt^
who was probably better acquainted with the works of agriculturists
than almost any other individual, and who was himself a very good
judge of animals, speaks of the principle of selection as " that which
enables the agriculturist, not only to modify the character of his
flock, but to change it altogether. It is the magician's wand, by
means of which he may summon into life whatever form and mould
he pleases." Lord Somerville, speaking of what breeders have dont
for sheep, says : — " It would seem as if they had chalked out upon
a wall a form perfect in itself, and then had given it existence." In
Saxony the importance of the principle of selection in regard to
merino sheep is so fully recognised, that men follow it as a trade :
the sheep are placed on a table and are studied, like a picture by a
connoisseur ; this is done three times at intervals of months, and the
sheep are each time marked and classed, so that the very best may
ultimately be selected for breeding.

What English breeders have actually effected is proved by the
enormous prices given for animals with a good pedigree ; and these
have been exported to almost every quarter of the world. The
improvement is by no means generally due to crossing different
breeds ; all the best breeders are strongly opposed to this practice,
except sometimes amongst closely allied sub-breeds. And when a
cross has been made, the closest selection is far m.ore indispensable
even than in ordinary cases. If selection consisted merely in sepa-
rating some very distinct variety, and breeding from it, the principle
would be so obvious as hardly to be worth notice ; but its import-
ance consists in the great effect produced by the accumulation in
one direction, during successive generations, of differences absolutely
inappreciable by an uneducated eye — differences which I for one
have vainly attempted to appreciate. Not one man in a thousand
has accuracy of eye and judgment sufficient to become an eminent
breeder. If gifted with these qualities, and he studies his subject
for years, and devotes his lifetime to it with indomitable perse-
verance, he will succeed, and may make great improvements ; if he
wants any of these qualities, he will assuredly fail. Few would
readily believe in the natural capacity and years of practice requisite
to become even a skilful pigeon-fancier.

The same principles are followed by horticulturists ; but the vari-
ations are here often more abrupt. No one suyjposes that our
choicest productions have been produced by a single variation from
the aboriginal stock. We have proofs that this has not been so in
eeveral cases in which exact records have been kept; thuu, to gJTe a

;etv,

24 METHODICAL SELECTION. [Chap. I.

very trifling instance, the steadily-increasing size of the common
gooseberry may be quoted. We see an astonishing improvement in
many florists' flowers, when the flowers of the present day are com«
pared with drawings made only twenty or thirty years ago. When
ft race of plants is once pretty well established, the seed-raisers do
not pick out the best plants, but merely go over their seed-bods,
and pull up the "rogues," as they call the plants that deviate
from the proper standard. With animals this kind of selection is,
in fact, likewise followed ; for hardly any one is so careless as to
breed from his worst animals.

In regard to plants, there is another means of observing the
accumulated effects of selection — namely, by comparing the diver-
sity of flowers in the different varieties of the same species in the
flower-garden ; the diversity of leaves, pods, or tubers, or whatever
part is valued, in the kitchen-garden, in comparison with the
flowers of the same varieties ; and the diversity of fruit of the same
species in the orchard, in comparison with the leaves and flowers
of the same set of varieties. See how different the leaves of the
cabbage are, and how extremely alike the flowers ; how unlike the
flowers of the heartsease are, and how alike the leaves; how much
the fruit of the different kinds of gooseberries differ in size, colour,
shape, and hairiness, and yet the flowers present very slight diffe-
rences. It is not that the varieties which differ largely in some one
point do not differ at all in other points ; this is hardly ever, — I
speak after careful observation, — perhaps never, the case. The law
of correlated variation, the importance of which should never be
overlooked, will ensure some differences ; but, as a general rule, it
cannot be doubted that the continued selection of slight variations,
either in the leaves, the flowers, or the fruit, will produce races dif-
fering from each other chiefly in these characters.

It may be objected that the principle of selection has been
reduced to methodical practice for scarcely more than three-quarters
of a century ; it has certainly been more attended to of late years,
and many treatises have been published on the subject ; and the
result has been, in a corresponding degree, rapid and important.
But it is very far from true that the principle is a modern discovery.
I could give several references to works of high antiquity, in which
the full importance of the principle is acknowledged. In rude and
barbarous periods of English history choice animals were cften im-
ported, and laws were passed to prevent their exportation : the
destruction of horses under a certain size was ordered, and this may
be compared to the " roguing " of plants by nurserymen. The prin-
ciple of selection I find distinctly given in an ancient Chinese encj-

^ 1 ^ /

Chap. I.] UNCONSCIOUS SELECnON.

clopsedia. Explicit rules are laid down by some of the Eoman
classical writers. From passages in Genesis, it is clear that the
colour of domestic animals was at that early period attended to.
Savages now sometimes cross their dogs with wild canine animals,
to improve the breed, and they formerly did so, as is attested by
passages in Pliny. The savages in South Africa match their
draught cattle by colour, as do some of the Esquimaux their teams
of dogs. Livingstone states that good domestic breeds are highly
valued by the negroes in the interior of Africa who have not associ-
ated with Europeans. Some of these facts do not show actual
selection, but they show that the breeding of domestic animals was
carefully attended to in ancient times, and is now attended to by
the lowest savages. It would, indeed, have been a strange fact, had
attention not been paid to breeding, for the inheritance of good and
bad qualities is so obvious.

Unconscious Selection,

At the present time, eminent breeders try by methodical selection,
with a distinct object in view, to make a new strain or sub-breed,
superior to anything of the kind in the country. But, for our pur-
pose, a form of Selection, which may be called Unconscious, and
which results from every one trying to possess and breed from the
best individual animals, is more important. Thus, a man who
intends keeping pointers naturally tries to get as good dogs as he
can, and afterwards breeds from his own best dogs, but he has no
wish or expectation of permanently altering the breed. Neverthe-
less we may infer that this process, continued during centuries,
would improve and modify any breed, in the same way as Bake-
well, Collins, &c., by this very same process, only carried on more
methodically, did greatly modify, even during their lifetimes, the
forms and qualities of their cattle. Slow and insensible changes of
this kind can never be recognised unless actual measurements or
careful drawings of the breeds in question have been made long ago^
which may serve for comparison. In some cases, however, un-
changed, or but little changed individuals of the same breed exist
in less civilised districts, where the breed has been less improved.
There is reason to believe that King Charles's spaniel has been un-
consciously modified to a large extent since the time of that monarch.
Some highly competent authorities are convinced that the setter is
directly derived from the spaniel, and has probably been slowly
altered from it. It is known that the English pointer has beeu
gi'eatly changed within the last century, and in this case the chauge
has, it is believed, been chiefly effected by crosses with the foxhound :

£6 UNCONSCIOUS SELECTION. [Chap, l,

but what concerns us is, that the change has been effected uncon*
Eciously and gradually, and yet so effectually, that, though the old
Spanish pointer certainly came from Spain, Mr. Borrow has not seen,
as I am informed by him, any native dog in Spain like our pointer.

By a similar process of selection, and by careful training, English
racehorses have come to surpass in fleetness and size the parent
Arabs, so that the latter, by the regulations for the Goodwood Races,
are favoured in the weights which they carry. Lord Spencer and
others have shown how the cattle of England have increased in
weight and in early maturity, compared with the stock formerly
kept in this country. By comparing the accounts given in various
old treatises of the former and present state of carrier and tumbler
pigeons in Britain, India, and Persia, we can trace the stages through
which they have insensibly passed, and come to differ so greatly
from the rock-pigeon.

Youatt gives an excellent illustration of the effects of a course of
selection, which may be considered as unconscious, in so far that the
breeders could never have expected, or even wished, to produce
the result which ensued — namely, the production of two distinct
strains. The two flocks of Leicester sheep kept by Mr. Buckley
and Mr. Burgess, as Mr. Youatt remarks, " have been purely bred
from the original stock of Mr. Bakewell for upwards of fifty years.
There is not a suspicion existing in the mind of any one at all
acquainted with the subject, that the owner of either of them has
deviated in any one instance from the pure blood of Mr. Bakewell's
flock, and yet the difference between the sheep possessed by these
two gentlemen is so great that they have the apjiearance of being
quite different varieties."

If there exist savages so barbarous as never to think of the inherited
character of the offspring of their domestic animals, yet any one
animal particularly useful to them, for any special purpose, would
be carefully preserved during famines and other accidents, to which
savages are so liable, and such choice animals would thus generally
leave more offspring than the inferior ones ; so that in this case
there would be a kind of unconscious selection going on. We see
the \ alue set on animals even by the barbarians of Tierra del Fuego,^
by their killing and devouring their old women, in times of dearth,
us of less value than their dogs.

In plants the same gradual process of improvement, through the
occasional preservation of the best individuals, whether or not
sufficiently distinct to be ranked at their first appearance as distinct
varieties, and whether or not two or more species or races have
become blended together by crossing, may plainly be recognised in

OiTAr. I.] UNCONSCIOUS SELECTION. 27

the increased size and beauty which we now see in the varieties of
the heartsease, rose, pelargonium, dahlia, and other plants, when
compared with the older varieties or with their parent-stocks. No
one would ever expect to get a first ->rate hearsease or dahlia from
the seed of a wild plant. No one would expect to raise a first-rate
melting pear from the seed of the wild pear, though he might
succeed from a poor seedling growing wild, if it had come from a
garden-stock. The pear, though cultivated in classical times,
appears, from Pliny's description, to have been a fruit of very
inferior quality. I have seen great surprise expressed in horti-
cultural works at the wonderful skill of gardeners, in having pro-
duced such splendid results from such poor materials ; but the art
has been simple, and, as far as the final result is concerned, has
been followed almost unconsciously. It has consisted in always
cultivating the best known variety, sowing its seeds, and, when a
slightly better variety chanced to appear, selecting it, and so on-
wards. But the gardeners cf the classical period, who cultivated
the best pears which they could procure, never thought what
splendid fruit we should eat ; though we owe our excellent fruit,
in some small degree, to their having naturally chosen and preserved
the best varieties they could anywhere find.

A large amount of change, thus slowly and unconsciously ac-
cumulated, explains, as I believe, the well-known fact, that in a
number of cases we cannot recognise, and therefore do not know,
the wild parent-stocks of the plants which have been longest culti-
vated in our flower and kitchen gardens. If it has taken centuries
or thousands of years to improve or modify most of our plants up to
their present standard of usefulness to man, we can understand how
it is that neither Australia, the Cape of Good Hope, nor any other
region inhabited by quite uncivilised man, has afforded us a single
plant worth culture. It is not that these countries, so rich in species,
do not by a strange chance possess the aboriginal stocks of any use-
ful plants, but that the native plants have not been improved by
continued selection up to a standard of perfection comparable with
that acquired by the plants in countries anciently civilised.

In regard to the domestic animals kept by uncivilised man, it
should not be overlooked that they almost always have to struggle
for their own food, at least during certain seasons. And in two
countries very differently circumstanced, individuals of the sarue
species, having slightly different constitutions or stnicture, would
orten succeed better in the one country than in the other ; and thus
by a process of " natural selection," as will hereafter be more fully
explained, two sub-breeds might be formed. This, f>erhap8, partly

28 UNCONSCIOUS SELECTION. [Chap. 1.

explains v:hj the varieties kept by savages, as has been remarked
by some authors, have more of the character of true species than the
varieties kept in civilised countries.

On the view here given of the important part which selection by
man has played, it becomes at once obvious, how it is that our
domestic races show adaptation in their structure or in their habits
to man's wants or fancies. We can, I think, further understand the
frequently abnormal character of our domestic races, and likewise
their differences being so great in external characters, and relatively
so slight in internal parts or organs. Man can hardly select, or
only with much difficulty, any deviation of structure excepting such
as is externally visible ; and indeed he rarely cares for what is
internal. He can never act by selection, excepting on variations
which are first given to him in some slight degree by nature. No
man would ever try to make a fantail till he saw a pigeon with
a tail developed in some slight degree in an unusual manner, or a
pouter till he saw a pigeon w^ith a crop of somewhat unusual size;
and the more abnormal or unusual any character was when it first
appeared, the more likely it would be to catch his attention. But
to use such an expression as trying to make a fantail, is, I have no
doubt, in most cases, utterly incorrect. The man who first selected
a pigeon with a slightly larger tail, never dreamed what the descend •
ants of that pigeon would become through long-continued, partly?
unconscious and partly methodical, selection. Perhaps the parent-
bird of all fantails had only fourteen tail-feathers somewhat expanded,
like the present Java fantail, or like individuals of other and distinct
breeds, in which as many as seventeen tail-feathers have been
counted. Perhaps the first pouter-pigeon did not inflate its crop
much more than the turbit now does the upper part of its oeso-
phagus,— a habit which is disregarded by all fanciers, as it is not
one of the points of the breed.

Nor let it be thought that some great deviation of structure
would be necessary to catch the fancier's eye : he perceives ex-
tremely small differences, and it is in human nature to value slyij
novelty, however slight, in one's own possession. Nor must the
value which would formerly have been set on any slight difierences
in the individuals cf the same species, be judged of by the value
which is now set on them, after several breeds have fairly been
established. It is known that with pigeons many slight variations
now occasionally appear, but these are rejected as faults or devia-
tions from the standard of perfection in each breed. The common
goose has not given rise to any marked varieties ; hence the Tou-
louse and the common breed, which differ only in colour, that most

144

01!

Chap. I.J CIRCUMSTANCES FAVOURABLE TO SELECTION. 29

fleeting of characters, have lately been exhibited as distinct at our
poultry-shows.

These views appear to explain what has sometimes been noticed
— namely, that we know hardly anything about the origin or history
of any of our domestic breeds. But, in fact, a breed, like a dialect
of a language, can hardly be said to have a distinct origin. A man
preserves and breeds from an individual with some slight deviation
of structure, or takes more care than usual in matching his best
animals, and thus improves them, and the improved animals slowly
spread in the immediate neighbourhood. But they will as yet
hardly have a distinct name, and from being only slightly valued,
their history will ha;re been disregarded. When further improved
by the same slow and gradual process, they will spread more widely,
and will be recognised as something distinct and valuable, and will
then probably first receive a provincial name. In semi-civilised
countries, with little free communication, the spreading of a new
sub-breed would be a slow process. As soon as the points of value
are once acknowledged, the principle, as I have called it, of un-
conscious selection will always tend, — perhaps more at one period
than at another, as the breed rises or falls in fashion, — perhaps more
in one district than in another, according to the state of civilisation
of the inhabitants, — slowly to add to the characteristic features of
the breed, whatever they may be. But the chance will be infinitely
small of any record having been preserved of such slow, varying,
and insensible changes.

Circumstances favourable to Man's Power of Selection.

I will now say a few words on the circumstances, favourable, or
the reverse, to man's power of selection. A high degree of vari-
ability is obviously favourable, as freely giving the materials for
selection to work on ; not that mere individual differences are not
amply sufficient, with extreme care, to allow of the accumulation
of a large amount of modification in almost any desired direction.
But as variations manifestly useful or pleasing to man appear
only occasionally, the chance of their appearance will be much
increased by a large number of individuals being kept. Hence,
number is of the highest importance for success. On this principle
Marshall formerly remarked, with respect to the sheep of parts of
Yorkshire, " as they generally belong to poor people, and are mostly
in small lots, they never can be improved." On the other hand,
nurserymen, from keeping large stocks of the same plant, are gener-
ally far more successful than amateurs in raising new and valuable
varieties A large number of individuals of an animal or plant car

30 CIRCUMSTANCES FAVOURABLE TO SELECTION. [Chap, h

be reared only wtere the conditions for its propagation are favour-
able, When the individuals are scanty, all will be allovrcd to breed,
whatever their quality may be, and this will effectually prevent
selection. But probably the most important element is that the
animal or plant should be so highly valued by man, that the closest
attention is paid to even the slightest deviations in its qiLalities or
structure. Unless such attention be paid nothing can be effected,
I have seen it gravely remarked, that it was most fortunate that
the strawberry began to vary just when gardeners began to attend
to this plant. No doubt the strawberry had always varied since
it was cultivated, but the slight varieties had been neglected. As
soon, however, as gardeners picked out individual plants with
slightly larger, earlier, or better fruit, and raised seedlings from
them, and again picked out the best seedlings and bred from them,
then (with some aid by crossing distinct species) those many
admirable varieties of the strawberry were raised which have ap-
peared during the last half-century.

With animals, facility in preventing crosses is an important
element in the formation of new races, — at least, in a country
which is already stocked with other races. In this respect en-
closure of the land plays a part. Wandering savages or the in-
habitants of open plains rarely possess more than one breed of the
same species. Pigeons can be mated for life, and this is a great
^convenience to the fancier, for thus many races may be improved
and kept true, though mingled in the same aviary ; and this cir-
cumstance must have largely favoured the formation of new breeds.
Pigeons, I may add, can be propagated in great numbers and at a
very quick rate, and inferior birds may be freely rejected, as when
killed they serve for food. On the other hand, cats, from their
nocturnal rambling habits, cannot be easily matched, and, although
so much valued by women and children, we rarely see a distinct
breed long kept up ; such breeds as we do sometimes see are almost
always imported from some other country. Although I do not
doubt that some domestic animals vary less than others, yet the
rarity or absence of distinct breeds of the cat, the donkey, peacock,
goose, (fee, may be attributed in main part to selection not having
been brought into play : in cats, from the difficulty in pairing them ;
in donkeys, from only a few being kept by poor people, and little
attention paid to their breeding ; for recently in certain parts of
Spain and of the United States this animal has been surprisingly
modified and improved by careful selection : in peacocks, from not
being very easily reared and a large stock not kept : in geese, from
bsing valuable only for two purposes, food and feathers, and more

Chap. LI CIRCUMSTANCES FAVOURABLE TO SELECTION. 31

especially from no pleasure having been felt in the display of distinct
breeds ; but the goose, under the conditions to which it is exposed
\ihen domesticated, seems to have a singularly inflexible organisa-
tion, though it has varied to a slight extent, as I have elsewhere
described.

Some authors have maintained that the amount of variation in
our domestic productions is soon reached, and can never afterwards
be exceeded. It would be somewhat rash to assert that the limit
has been attained in any one case ; for almost all our animals and
plants have been greatly improved in many ways within a recent
period ; and this implies variation. It would be equally rash to
assert that characters now increased to their utmost limit, could
not, after remaining fixed for many centuries, again vary under
new conditions of life. No doubt, as Mr. Wallace has remarked
with much truth, a limit will be at last reached. For instance,
there must be a limit to the fleetness of any terrestrial animal, as
this will be determined by the friction to be overcome, the weight
of body to be carried, and the powxr of contraction in the muscular
fibres. But what concerns us is that the domestic varieties of the
same species differ from each other in almost eveiy character, which
man has attended to and selected, more than do the distinct species
of the same genera. Isidore Geoffrey St. Hilaire has proved this in
regard to size, and so it is with colour and probably with the length
of hair. With respect to fleetness, which depends on many bodily
characters, Eclipse was far fleeter, and a dray-horse is incomparably
S'fcronger than any two natural species belonging to the same
genus. So with plants, the seeds of the different varieties of the
bean or maize probably differ more in size, than do the seeds of
the distinct species in any one genus in the same two families.
The same remark holds good in regard to the fruit of the several
varieties of the plum, and still more strongly with the melon, as
well as in many other analogous cases.

To sum up on the origin of our domestic races of animals and
plants. Changed conditions of life are of the highest importance in
causing variability, both by acting directlj'' on the organisation, and
indirectly by affecting the reproductive system. It is not probable
that variability is an inherent and necessary contingent, under all
circumstances. The greater or less force of inheritance and rever-
sion determine whether variations shall endure. Variability is
governed by many unknown laws, of which correlated growth is
probably the most important. Something, but how much we do
net know, may be attributed to the definite action of the conditions
?f life. Some, perhaps a great, efi'ect may be attributed to the

32 SUMMARY OF SELECTION. [Chap. 1

Increased use or disnse of parts. The final result is thus rendered
infinitely com])lex. In some cases the intercrossing of aboriginally
distinct species appears to have played an important part in the
origin of our breeds. When several breeds have once been formed
in any country, their occasional intercrossing, with the aid of selec^
tion, has, no doubt, largely aided in the formation of new sub-
breeds ; but the importance of crossing has been much exaggerated,
both in regard to animals and to those plants which are pro-
pagated by seed. With plants which are temporarily propagated
by cuttings, buds, &c., the importance of crossing is immense ; for
the cultivator may here disregard the extreme variability both of
hybrids and of mongrels, and the sterility of hybrids ; but plants
Qot propagated by seed are of little importance to us, for their
endurance is only temporary. Over all these causes of Change, the
accumulative action of Selection, whether applied methodically and
quickly, or unconsciously and slowly but more efficiently, scorns to
have been the predominant rov\'er.

Chap. IL] VARIATION UNDER NATURE. 33

CHAPTEB IL

Yaiiiation under Nature.

Variability — Individual differences — Doubtful species — Wide ranging,
much diffused, and common species, vary most — Species of the larger
genera in each country vary more frequently than the species of the
smaller genera — Many of the species of the larger genera i*esemble
varieties in being very closely, but unequally, related to each other,
and in having restricted ranges.

Before applying the principles arrived at in the last chapter to
organic beings in a state of nature, we must briefly discuss whether
these latter are subject to any variation. To treat this subject
properly, a long catalogue of dry facts ought to be given ; but these
I shall reserve for a future work. Nor shall I here discuss the
-various definitions which have been given of the term species. No
one definition has satisfied all naturalists; yet every naturalist
knows vaguely what he means when he speaks of a species.
Generally the term includes the unknown element of a distinct
act of creation. The term " variety " is almost equally difficult
to define; but here community of descent is almost universally
implied, though it can rarely be proved. We have also what
are called monstrosities ; but they graduate into varieties. By
a monstrosity I presume is meant some considerable deviation of
structure, generally injurious, or not useful to the species. Some
authors use the term " variation " in a technical sense, as implying
a modification directly due to the physical conditions of life ; and
" variations " in this sense are supposed not to be inherited ; but
who can say that the dwarfed condition of shells in the brackish
waters of the Baltic, or dwarfed plants on Alpine summits, or the
thicker fur of an animal from far northwards, would not in some
cases be inherited for at least a few generations ? and in this case I
presume that the form would be called a variety.

It may be doubted whether sudden and considerable deviations
«f structure such as we occasionally see in our domestic productions,
more especially with plants, are ever pennanently propagated in a
fitate of nature. Almost every part of every organic being is so
beautifully related to its complex conditions of life that it seems as

D

34 INDIVIDUAL DIFFERENCES. [Chap. II.

impro'bable that any part should have been suddenly produced
perfect, as that a complex machine should have been invented by
man in a perfect state. Under domestication monstrosities some-
times occur which resemble normal structures in widely diiTerent
animals. Thus pigs have occasionally been born with a sort of
proboscis, and if any wild species of the same genus had naturally
possessed a proboscis, it might have been argued that this had
appeared as a monstrosity ; but I have as yet failed to find, after
diligent search, cases of monstrosities resembling normal structures
in nearly allied forms, and these alone bear on the question. If
monstrous forms of this kind ever do appear in a state of nature and
are capable of reproduction (which is not always the case), as they
occur rarely and singly, their preservation would depend on
unusually favourable circumstances. They would, also, during the
first and succeeding generations cross with the ordinary form, and
thus their abnormal character would almost inevitably be lost.
But I shall have to return in a future chapter to the preservation
and perpetuation of single or occasional variations.

Individual Differences.

The many slight differences which appear in the offspring from
the same parents, or which it may be presumed have thus arisen,
from being observed in the individuals of the same species in-
habiting the same confined locality, may be called individual
differences. No one supposes that all the individuals of the same
species are cast in the same actual mould. These individual
differences are of the highest importance for us, for they are often
inherited, as must be familiar to every one ; and they thus afford
materials for natural selection to act on and accumulate, in the
same manner as man accumulates in any given direction individual
differences in his domesticated productions. These individual
differences generally affect what naturalists consider unimportant
parts ; but I could show by a long catalogue of facts, that parts
which must be called important, whether viewed under a physio-
logical or classificatory point of view, sometimes vary in the
individuals of the same species. I am convinced that the most
experienced naturalist would be surprised at the number of the
cases of variability, even in important parts of structure, which ho
could collect on good authority, as I have collected, during a course
of years. It should be remembered that systematiSts are far from
being pleased at finding variability in important characters, and
that there are not many men who will laboriously examine internal
and important organs, and compare them in many specimens of

Chap. IJ.] INDIVIDUAL DIFFERENCES 35

the same species. It would never have been expected that the
branching of the main nerves close to the great central ganglion of
an insect would have been variable in the same species ; it migbt
have been thought that changes of this nature could have been
effected only by slow degrees ; yet Sir J. Lubbock has shown a
degree of variability in these main nerves in Coccus, which may
almost be compared to the irregular branching of the stem of a tree.
This philosophical naturalist, I may add, has also shown that the
muscles in the larvse of certain insects are far from uniform.
Authors sometimes argue in a circle when they state that important
organs never vary ; for these same authors practically rank those
parts as important (as some few naturalists have honestly confessed)
which do not vary ; and, under this point of view, no instance will
ever be found of an important part varying ; but under any other
point of view many instances assuredly can be given.

There is one point connected with individual differences, which is
extremely perplexing : I refer to those genera which have been called
" protean " or " polymorphic," in which the species present an inor-
dinate amount of variation. With respect to many of these forms,
hardly two naturalists agree whether to rank them as species or as
varieties. We may instance Rubus, Rosa, and Hieracium amongst
plants, several genera of insects and of Brachiopod shells. In most
polymorphic genera some of the species have fixed and definite
characters. Genera which are polymorphic in one country seem to
be, with a few exceptions, polymorphic in other countries, and like-
wise, judging from Brachiopod shells, at former periods of time.
These facts are very perplexing, for they seem to show that this
kind of variability is independent of the conditions of life. I am
inclined to suspect that we see, at least in some of these polymorphio
genera, variations which are of no service or disservice to the species,
and which consequently have not been seized on and rendered definite
by natural selection, as hereafter to be explained.

Individuals of the same species often present, as is known to
every one, great differences of structure, independently of variation,
as in the two sexes of various animals, in the two or three castes of
sterile females or workers amongst insects, and in the immature and
larval states of many of the lower animals. There are, also, cases
of dimorphism and trimorphism, both with animals and plants.
Thus, Mr. Wallace, who has lately called attention to the subject,
has shown that the females of certain species of butterflies, in the
Malayan archipelago, regularly appear under two or even three
conspicuously distinct forms, not connected by intermediate varieties.
"Fritz Miiller has described analagous but more extraordinary cases

D 2

38 DOUBTFUL SPECIES. [Chap. II

ferences are seen to be so slight and graduated, that- it is impossible
to define or describe them, though at the samo time the extreme
forms are sufficiently distinct. The geographical races or sub-species
are local forms completely fixed and isolated ; but as they do not
differ from each other by strongly marked and important characters,
*' there is no possible test but individual opinion to determine
which of them shall be considered as species and which as varieties.*'
Lastly, representative species fill the same place in the natural
economy of each island as do the local forms and sub-species ; but
as they are distinguished from each other by a greater amount of
difference than that between the local forms and sub-species, they
are almost universally ranked by naturalists as true species. Never-
theless, no certain criterion can possibly be given by which variable
forms, local forms, sub-species, and representative species can be
recognised.

Many years ago, when comparing, and seeing others compare, the
birds from, the closely neighbouring islands of the Galapagos archi-
pelago, one with another, and with those from the American main-
land, I was much struck how entirely vague and arbitrary is the
distinction between species and varieties. On the islets of the
little Madeira group there are many insects which are charac-
terized as varieties in Mr. Wollaston's admirable work, but
which would certainly be ranked as distinct species by many
entomologists. Even Ireland has a few animals, now generally
regarded as varieties, but which have been ranked as species
by some zoologists. Several experienced ornithologists consider
our British red grouse as only a strongly-marked race of a
Norwegian species, whereas the greater number rank it as an
undoubted species peculiar to Great Britain. A wide distance
between the homes of two doubtful forms leads many naturalists to
rank them as distinct species ; but what distance, it has been well
asked, will suffice ; if that between America and Europe is ample,
will that between Europe and the Azores, or Madeira, or the
Canaries, or between the several islets of these small archipelagos,
be sufficient ?

Mr. B. D. Walsh, a distinguished entomologist of the United
States, has described what he calls Phytophagic varieties and Phy-
tophagic species. Most vegetable-feeding insects live on one kind
of plant or on one group of plants ; some feed indiscriminately on
many kinds, but do not in consequence vary. In several cases,
however, insects found living on different plants, have been observed
by Mr. Walsh to present in their larval or mature state, or in both
states, slig:ht, though constant differences in colour, size, or in the

Chap. II.] DOUBTFUL SPECIES. 30

nature of tlieir secretions. In some instances tlie males alone, in
ether instances both males and females, have been observed thus
10 differ in a slight degree. When the differences are rather more
strongly marked, and when both sexes and all ages are affected, thflr*^
forms are ranked by all entomologists as good species. But no
observer can determine for another, even if he can do so for himself,
wliich of these Phytophagic forms ought to be called species and
which varieties. Mr. Walsh ranks the forms which it may be
supposed would freely intercross, as varieties; and those which
appear to have lost this power, as species. As the differences depend
on the insects having long fed on distinct plants, it cannot be
expected that intermediate links connecting the several forms should
now be found. The naturalist thus loses his best guide in deter-
mining whether to rank doubtful forms as varieties or species. This
likewise necessarily occurs with closely allied organisms, which
inhabit distinct continents or islands. When, on the other hand,
an animal or plant ranges over the same continent, or inhabits many
islands in the same archipelago, and presents different forms in the
different areas, thers is always a good chance that intermediate
foims will be discovered which will link together the extreme
states ; and these are then degraded to the rank of varieties.

Some few naturalists maintain that animals never present varie-
ties ; but then these same naturalists rank the slightest difference
as of specific value ; and when the same identical form is met with
in two distant countries, or in two geological formations, they
believe that two distinct species are hidden under the same dress.
The term species thus comes to be a mere useless abstraction, im-
plying and assuming a separate act of creation. It is certain that
many forms, considered by highly-competent judges to be varieties,
resemble species so completely in character, that they have been thus
ranked by other highly-competent judges. But to discuss whether
they ought to be called species or varieties, before any definition of
these terms has been generally accepted, is vainly to beat the air.

Many of the cases of strongly-marked varieties or doubtful species
well deserve consideration ; for several interesting lines of argument,
from geographical distribution, analogical variation, hybridism, &c.,
have been brought to bear in the attempt to determine their rank ;
but space does not here permit me to discuss them. Close investi-
gation, in many cases, will no doubt bring naturalists to agree how
to rank doubtful forms. Yet it must be confessed that it is in the
host known countries that we find the greatest number of them.
I have been struck with the fact, that if any animal or plant in a
state of nature be highly useful to man, or from any cause closely

40 DOUBTFUL SPECIES. [Chap. II,

attracts his attention, varieties of it will alii.ost universally be
found recorded. These varieties, moreover, will often be ranked by
some authors as species. Look at the common oak, how closely it
has been studied ; yet a German author makes more than a dozen
species out of forms, which are almost universally considered by
other botanists to be varieties ; and in this country the highest
botanical authorities and practical men can be quoted to show that
the sessile and pedunculated oaks are either good and distinct species
or mere varieties.

I may here allude to a remarkable memoir lately published by
A. de CandoUe, on the oaks of the whole world. No one ever had
more ample materials for the discrimination of the species, or could
have worked on them with more zeal and sagacity. He first gives
in detail all the many points of structure which vary in the several
species, and estimates numerically the relative frequency of the
variations. He specifies above a dozen characters which may be
found varying even on the same branch, sometimes according to
age or development, sometimes without any assignable reason.
Such characters are not of course of specific value, but they are, as
Asa Gray has remarked in commenting on this memoir, such as
generally enter into specific definitions. De Candolle then goes on
to say that he gives the rank of species to the forms that differ by
characters never varying on the same tree, and never found con-
nected by intermediate states. After this discussion, the result of
so much labour, he emphatically remarks : " They are mistaken,
who repeat that the greater part of our species are clearly limited,
and that the doubtful species are in a feeble minority. This seemed
to be true, so long as a genus was imperfectly known, and its species
were founded upon a few specimens, that is to say, were provisionaL
Just as we come to know them better, intermediate forms flow in,
and doubts as to specific limits augment." He also adds that it is
the best known species which present the greatest number of spon-
taneous varieties and sub- varieties. Thus Quercus robur has twenty-
3ight varieties, all of which, excepting six, are clustered round three
sub-species, namely, Q. pedunculata, sessiliflora, and pubescens.
The forms which connect these three sub-species are comparatively
rare ; and, as Asa Gray again remarks, if these connecting forms,
which are now rare, were to become wholly extinct, the three sub-
species would hold exactly the same relation to each other, as do
the four or five provisionally admitted species which closely sur-
round the typical Quercus robur. Finally, De Candolle admits
that out of the 300 species, which will be et.umerated in his Pro-
dromus as belonging to the oak family, at least two-thirds are

. IIAP. II.J DOUBTFUL SPECIES. 41

provisional species, that is, arc not known strictly to fulfil the defi-
nition above given of a true species. It should he added that De
CandoUe no longer believes that species are immutable creations, but
concludes that the derivative theory is the most natural one, " and
the most accordant with the known facts in palaaontology, geo-
graphical botany and zoology, of anatomical structure and classifi-
cation."

When a young naturalist commences the study of a group of
organisms quite imknown to him, he is at first much perplexed in
determining what differences to consider as specific, and what as
varietal ; for he knows nothing of the amount and kind of variation
to which the group is subject ; and this shows, at least, how very
generally there is some variation. But if he confine his attention
to one class within one country, he will soon make up his mind
how to rank most of the doubtful forms. His general tendency
will be to make many species, for he will become impressed, just
like the pigeon or poultry fancier before alluded to, with the amount
of difference in the forms which he is continually studying ; and
he has little general knowledge of analogical variation in other
groups and in other countries, by which to correct his first impres-
sions. As he extends the range of his observations, he will meet
with more cases of difficulty; for he will encounter a greater
number of closely-allied forms. But if his observations be widely
extended, he will in the end generally be able to make up his own
mind ; but he will succeed in this at the expense of admitting much
variation, — and the truth of this admission will often be disputed
by other naturalists. When he comes to study allied forms brought
from countries not now continuous, in which case he cannot hope
to find intermediate links, he will be compelled to trust almost
entirely to analogy, and his difficulties will rise to a climax.

Certainly no clear line of demarcation has as yet been drawn
between species and sub-species — that is, the forms which in the
opinion of some naturalists come very near to, but do not quite
arrive at, the rank of species : or, again, between sub-species and
well-marked varieties, or between lesser varieties and individual dif-
ferences. These differences blend into each other by an insensible
series ; and a series impresses the mind with the idea of an actual
passage.

Hence I look at individual differences, though of small interest to
the systematist, as of the highest importance for us, as being the
first steps towards such slight varieties as are barely thought worth
recording in works on natural history. And I look at varieties
which arc in any degree more distinct and permanent, as stepa

42 DOMi:,^iNT SPECIES VARY MOST. [Chap. II.

towards more strongly-marked and permanent varieties ; and at tlie
latter, as leading to sub-species, and then to species. The passage
from one stage of difference to another may, in manji cascy, be the
simple result of the nature of the organism and of the different
physical conditions to which it has long been exposed ; but with
respect to the more important and adaptive characters, the passage
from one stage of difference to another, may be safely attributed to
the cumulative action of natural selection, hereafter to be explained,
and to the effects of the increased use or disuse of parts. A well-
marked variety may therefore be called an incipient species ; but
whether this belief is justifiable must be judged by the weight
of the various facts and considerations to be given througnout this
work.

It need not be supposed that all varieties or incipient species
attain the rank of species. They may become extinct, or they may
endure as varieties for very long periods, as has been shown to be
the case by Mr. Wollaston with the varieties of certain fossil land-
shells in Madeira, and with plants by Gaston de Saporta. If a
variety were to flourish so as to exceed in numbers the parent
species, it would them rank as the species, and the species as tho
variety ; or it might come to supplant and exterminate the parent
species; or both might co-exist, and both rank as independent
species. But we shall hereafter return to this subject.

From these remarks it will be seen that I look at the term species
as one arbitrarily given, for the sake of convenience, to a set of
individuals closely resembling each other, and that it does not
essentially differ from the term variety, which is given to less
distinct and more fluctuating forms. The term variety, again, in
comparison with mere individual differences, is also applied arbi-
trarily, for convenience' sake.

Wide-ranging J muchrdiffusedj and common Species vary most.

Guided by theoretical considerations, I thought that some in-
teresting results might be obtained in regard to the nature and
relations of the species which vary most, by tabulating all the
varieties in several well-worked floras. At first this seemed a
simple task ; but Mr. H. C. Watson, to whom I am much indebted
for valuable advice and assistance on this subject, soon convinced
me that there were many difficulties, as did subsequently Dr
Hooker, even in stronger terms. I shall reserve for a future work
the discussion of these difficulties, and the tables of the proportional
numbers of the varying species. Dr. Hooker permits me to add,
that after having carefully read my manuscript, and examined the

Chap. II.] DOMINANT SPECIES VARY MOST. 43

tables, lie thinks that the following statements are fairly well esta-
blished. The whole subject, however, treated as it necessarily here
is with much brevity, is rather perplexing, and allusions cannot bo
avoided to the " f truggle for existence," " divergence of character,"
and other questions, hereafter to be discussed.

Alphonse de CandoUe and others have shown that plants which
have very wide ranges generally present varieties ; and this might
have been expected, as they are exposed to diverse physical condi-
tions, and as they come into competition (which, ss we shall here-
after see, is an equally or more important circumstance) with
different sets of organic beings. But my tables further show that,
in any limited country, the species which are the most common,
that is abound most in individuals, and the species which are most
widely diffused within their own country (and this is a different
consideration from wide range, and to a certain extent from com-
monness), oftenest give rise to varieties sufficiently well-marked
to have been recorded in botanical works. Hence it is the most
flourishing, or, as they may be called, the dominant species, — those
which range widely, are the most diffused in their own country, and
are the most numerous in individuals, — which oftenest produce
well-marked varieties, or, as I consider them, incipient species. And
this, perhaps, might have been anticipated ,■ for, as varieties, in
order to become in any degree permanent, necessarily have to
struggle with the other inhabitants of the country, the species which
are already dominant will be the most likely to yield offspring,
which, though in some slight degree modified, still inherit those
advantages that enabled their parents to become dominant over
their compatriots. In these remarks on predominance, it should be
understood that reference is made only to the forms which come
into competition with each other, and more especially to the mem-
bers of the same genus or class having nearly similar habits of life.
With respect to the number of individuals or commonness ol
species, the comparison of course relates only to the members
of the same group. One of the higher plants may be said to be
dominant if it be more numerous in individuals and more widely
diffused than the other plants of the same country, which live under
Dearly the same conditions. A plant of this kind is not the less
dominant because some conferva inhabiting the water or some
parasitic fungus is infinitely more numerous in individuals, and more
widely diffused. But if the conferva or parasitic fungus exceeds its
alUes in the above respects, it will then be dominant within its own
clas».

44 SPECIES OF LARGER GENERA VARIABLE. [Chap. 11,

Spscies of the Larger Genera in each Country vary more frequenUy
than the Species of the Smaller Genera.

If the plants inhabiting a country, as described in any Flora, be
divided into two equal masses, all those in the larger genera (i.e.,
those including many species) being placed on one side, and all
those in the smaller genera on the other side, the former will bo
foujid to include a somewhat larger number of the very common and
much diffused or dominant species. This might have been antici-
pated ; for the mere fact of many species of the same genus inhabit-
ing any country, shows that there is something in the organic or
inorganic conditions of that country favourable to the genus ; and,
consequently, we might have expected to have found in the larger
genera, or those including many species, a larger proportional number
of dominant species. But so many causes tend to obscure this
result, that I am surprised that my tables show even a small majority
on the side of the larger genera. I will here allude to only two
causes of obscurity. Fresh-water and salt-loving plants generally
have very wide ranges and are much diffused, but this seems to be
connected with the nature of the stations inhabited by them, and
has little or no relation to the size of the genera to which the
species belong. Again, plants low in the scale of organisation are
generally much more widely diffused than plants higher in the scale j
and here again there is no close relation to the size of the genera.
The cause of lowly-organised plants ranging widely will be discussed
in our chapter on Geographical Distribution.

From looking at species as only strongly-marked and well-defined
varieties, I was led to anticipate that the species of the larger genera
in each country would oftener present varieties, than the species of
the smaller genera ; for wherever many closely related species (i.e.,
species of the same genus) have been formed, many varieties or
incipient species ought, as a general rule, to be now forming.
Where many large trees grow, we expect to find saplings. Whero
many species of a genus have been formed through variation, cir-
cumstances have been favourable for variation ; and hence we might
expect that the circumstances would generally be still favourable
to variation. On the other hand, if we look at each species as a
special act of creation, there is no apparent reason why more
varieties should occur in a group having many species, than in one
having lew.

To test the truth of this anticipation I have arranged the plants
of twelve countries, and the coleopterous insects of two districts, into
two nearly equal masses, the species of the larger genera on one

Chaf. II.] SPECIES OF LARGER GENERA VARIABLE. 45

side, and those of the smaller genera on the other side, and it has
invariably proved to be the case that a larger proportion of the
species on the side of the larger genera presented varieties, than on
the side of the smaller genera. Moreover, the species of the large
genera which present any varieties, invariably present a larger
average number of varieties than do the species of the small genera.
Both these results follow when another division is made, and when
all the least genera, with from only one to four species, are altogether
excluded from the tables. These facts are of plain signification on
the view that species are only strongly-marked and permanent
varieties ; for wherever many species of the same genus have been
formed, or where, if we may use the expression, the manufactory of
species has been active, we ought generally to find the manufactory
still in action, more especially as we have every reason to believe
the process of manufacturing new species to be a slow one. And
this certainly holds true, if varieties be looked at as incipient species ;
for my tables clearly show as a general rule that, wherever many
species of a genus have been formed, the species of that genus
present a number of varieties, that is of incipient species, beyond
the average. It is not that all large genera are now varying much,
and are thus increasing in the number of their species, or that no
small genera are now varying and increasing ; for if this had been
so, it would have been fatal to my theory ; inasmuch as geology
plainly tells us that small genera have in the lapse of time often
increased greatly in size ; and that large genera ?iave often come to
their maxima, declined, and disappeared. All that we want to show
is, that, where many species of a genus have been formed, on an
average many are still forming ; and this certainly holds good.

Many of the Species induded within the Larger Genera resemble
^ Varieties in heing very closely, but unequally, related to each
■ other, and in having restricted ranges.

There are other relations between the species of large genera and
their recorded varieties which deserve notice. We have seen that
there is no infallible criterion by which to distinguish species and
well-marked varieties ; and when intermediate links have not been
found between doubtful forms, naturalists arc compelled to come to
a determination by the amount of difference between them, judging
\)y analogy whether or not the amount sufiBces to raise one or both
to the rank of species. Hence the amount of difference is one very
important criterion in settling whether two forms should be ranked
as species or varieties. Now Fries has remarked in regard to plants,
and Westwood in regard to insects, that in large genera the amount

46 SPECIES OF LARGER GENERA [Chap. II.

of difference between the species is often exceedingly small. I have
endeavoured to test this numerically by averages, and, as far as my
imperfect results go, they coRfirm the view. I have also consulted
some sagacious and experienced observers, and, after deliberation^
they concur in this view. In this respect, therefore, the species
of the larger genera resemble varieties, more than do the species oi
the smaller genera. Or the case may be put in another way, and it
may be said, that in the larger genera, in which a number of varie-
ties or incipient species greater than the average are now manufac-
turing, many of the species already manufactured still to a certain
extent resemble varieties, for they differ from each other by less
than the usual amount of difference.

Moreover, the species of the larger genera are related to each
other, in the same manner as the varieties of any one species are
related to each other. No naturalist pretends that all the species of
a genus are equally distinct from each other ; they may generally
be divided into sub-genera, or sections, or lesser groups. As Fries
has well remarked, little groups of species are generally clustered
like satellites around other species. And what are varieties but
groups of forms, unequally related to each other, and clustered round
certain forms — that is, round their parent-species. Undoubtedly
there is one most important point of difference between varieties
and species ; namely, that the amount of difference between varie-
ties, when compared with each other or with their parent-species, is
much less than that between the species of the same genus, liut whcji
we come to discuss the principle, as I call it, of Divergence of
Character, we shall see how this may be explained, and how the
lesser differences between varieties tend to increase into the greater
differences between species.

There is one other point which is worth notice. Varieties gene-
rally have much restricted ranges ; this statement is indeed
scarcely more than a truism, for, if a variety were found to have a
wider range than that of its supposed parent-species, their denomi-
nations would be reversed. But there is reason to believe that the
species which are very closely allied to other species, and in so far
resemble varieties, often have much restricted ranges. For instance,
Mr. H. C. Watson has marked for me in the well-sifted London
Catalogue of plants (4th edition) 63 plailts which are therein ranked
as species, but which he considers as so closely allied to other
species as to be of doubtful value : these 63 reputed species range
on an average over 6*9 of the provinces into which Mr. Watson has
divided Great Britain. Now, in this same Catalogue, 53 acknow-
ledged varieties are recorded, and these range over 77 provinces;

Chap. II."] RESEMBLE VARIETIEC. 4*5

whereas, the species to which these varieties belong range over 14*3
provinces. So that the acknowledged varieties have nearly the same
restricted average range, as have the closely allied forms, marked
for me by Mr. Watson as doubtful species, but which are almost
universally ranked by British botanists as good and true species.

Summary.

Finally, varieties cannot be distinguished from species, — except,
first, by the discovery of intermediate linking forms ; and, secondly,
by a certain indefinite amount of difference between them ; for two
forms, if differing very little, are generally ranked as varieties, not-
withstanding that they cannot be closely connected; but the amount
of difference considered necessary to give to any two forms the rank
of species cannot be defined. In genera having more than the average
number of species in any cov iitry, the species of these genera have
more than the average number of varieties. In large genera the
species are apt to be closely, but unequally, allied together, forming
little clusters round other species. Species very closely allied to
other species apparently have restricted ranges. In all these respects
the species of large genera present a strong analogy with varieties.
And we can clearly understand these analogies, if species once
existed as varieties, and thus originated ; whereas, these analogies
are utterly inexplicable if species are independent creations.

We have, also, seen that it is the most flourishing or dominant
species of the larger genera within each class which on an average
yield the greatest number of varieties ; and varieties, as we shall
hereafter see, tend to become converted into new and distinct
species. Thus the larger genera tend to become larger ; and through-
out nature the forms of life which are now dominant tend to become
still more dominant by leaving many modified and dominant
descendants. But by steps hereafter to be explained, the larger
genera also tend to break up into smaller genera. And thus, the
forms of life throughout the universe become divided into groups
subordinate to groupj

4S STRUGGLE FOR EXISTENCE. [Chap. IIL

CHAPTEE III.

Struggle for Existence.

Its bearing on natural selection — The term used in a wide sense — Geome-
trical ratio of increase — Rapid increase of naturalised animals and
plants — Nature of the checks to increase — Competition universal — •
Effects of climate — Protection from the number of individuals —
Complex relations of all animals and plants throughout nature —
Struggle for life most severe between individuals and varieties of the
same species: often severe between species of the same genus — The
relation of organism to organism the most important of all relations.

Before entering on the subject of this chapter, I must make a few

preliminary remarks, to show how the struggle for existence bears

on Natural Selection. It has been seen in the last chapter that

amongst organic beings in a state of nature there is some individual

variability : indeed I am not aware that this has ever been disputed.

It is immaterial for us whether a multitude of doubtful forms be

called species or sub-species or varieties ; what rank, for instance, the

two or three hundred doubtful forms of British plants are entitled

to hold, if the existence of any well-marked varieties be admitted.

But the mere existence of individual variability and of some fev/

well-marked varieties, though necessary as the foundation for the

work, helps us but little in understanding how species arise in

nature. How have all those exquisite adaptations of one part of

the organisation to another part, and to the conditions of life, and

of one organic being to another being, been perfected? AVe see

/ these beautiful co-adaptations most plainly in the woodpecker and

/ the misletoe ; and only a little less plainly in the humblest parasite

' which clings to the hairs of a q'ladruped or feathers of a bird ; in

the structure of the beetle which dives through the water : in the

I plumed seed which is wafted by the gentlest breeze; in short, we

1 see beautiful adaptations everywhere and in every part of the

organic world.

Again, it may be asked, how is it that varieties, which I have
called incipient species, become ultimately converted into good and
distinct species, which in most cases obviously differ from each
other far more than do the varieties of the same species ? How do
those groups of species, which constitute what aro called distinct

Chap. 111.] STRUGGLE FOR EXISTENCK 49

g;«nera, and which differ from each other more than do the species
of the same genus, arise ? All these results, as we shall more fully
see in th© next chapter, follow from the struggle for life. Owing to
this struggle, variations, however slight, and from whatever cause-
proceeding, if they be in any degree profitable to the individuals of
a species, in their infinitely complex relations to other organic
beings and to their physical conditions of life, will tend to the
preservation of such individuals, and will generally be inherited
by the offspring. The offspring, also, wi^l thus have a better
chance of surviving, for, of the many individuals of any species
which are periodically born, but a small number can survive.
I have called this principle, by which each slight variation, if
useful, is . preserved, by the term Katural Selection, in order to
mark its relation to man's power of selection. But the expression
"oTten used by Mr. Herbert Spencer of the Survival of the Fittest
is more accurate, and is sometimes equally convenient. We have
seen that man by selection can certainly produce great results, and
can adapt organic beings to his own uses, through the accumulation
of slight but useful variations, given to him by the hand of Nature.
But Natural Selection, as we shall hereafter see, is a power inces-
santly ready for action, and is as immeasurably superior to man's
feeble efforts, as the works of Nature are to those of Art.

We will now discuss in a little more detail the struggle for
existence. In my future work this subject will be treated, as it
well deserves, at greater length. The elder De CandoUe and Lyell
have largely and philosophically shown that all organic beings arc
exposed to severe competition. In regard to plants, no one has
treated this subject with more spirit and ability than W. Herbert,
Dean of Manchester, evidently the result of his great horticultural
knowledge. Nothing is easier than to admit in words the truth of
the universal struggle for life, or more diflBcult — at least I have
found it so — than constantly to bear this conclusion in mind. Yet
unless it be thoroughly engrained in the mind, the whole economy
of nature, with every fact on distributiou, rarity, abundance, extinc-
tion, and variation, will be dimly seen or quite misunderstood.
We behold the face of nature bright with gladness, we often see
superabundance of food ; we do not see or we forget, tliat the birds »
which are idly singing round us mostly live on insects or seeds, and \
are thus constantly destroy in g life ; or we forget how largely these
songsters, or their eggs, or their nestlings, are destroyed by birds
and beasts of prey ; we do not always bear in mind, that, thougli
food may be now superabundant, it is not so at all seasons of oBch
recurring year.

E

V r c>L-Cr^ ^'^yK.^-^

60 GEOMETRICAL RATIO OF INCREASE.

^ w

R

5^

Tlie Term, Struggle for Existence, used in a large sense.

I should premise that I use this term in a large and metaphorical
sense inpluding dependence of one being on another, and including
(which is more important) not only the life of the individual, but
success in leaving progeny. Two canine animals, in a time of
dearth, may be truly said to struggle with each other which shall
get food and live. But a plant on the edge of a desert is said to
struggle for life against the drought, though more properly it should
be said to be dependent on the moisture. A plant which annually
produces a thousand seeds, of which only one on an average comes
to maturity, may be more truly said to struggle with the plants of
the same and other kinds which already clothe the ground. The
•jnisletoe is dependent on the apple and a few other trees, but can
only in a far-fetched sense be said to struggle with these trees, for,
if too many of these parasites grow on the same tree, it languishes
and dies. But several seedling misletoes, growing close together on
the same branch, may more truly be said to struggle with each
other. As the misletoe is disseminated by birds, its existence
depends on them ; and it may metaphorically be said to struggle
with other fruit-bearing plants, in tempting the birds to devour and
thus disseminate its seeds. In these several senses, which pass into
each other, I use for convenience' sake the general term of Struggle
for Existence.

Geometrical Ratio of Increase. L p-''''^'^^'t/^ 0

A struggle for existence inevitably follows from the high rate at
which all organic beings tend to increase. Every being, which
during its natural lifetime produces several eggs or seeds, must suffer
destruction during some period of its life, and during some season
or occasional year, otherwise, on the princij'le of geometrical increase,
its numbers would quickly become so inordinately great that no
country could support the product. Hence, as more individuals
are produced than can possibly survive, there must in every case
be a struggle for existence, either one individual Avitli another of

iM

the

same species,

or with the individuals of distinct species, or

with the physical conditions of life. It is the doctrine of Malthus
applied with manifold force to the whole animal and vegetable
kingdoms ; for in this case there can be no artificial increase of food,
and no prudential restraint from marriage. Although some species
may be now increasing, more or less rapidly, in numbers, all cannot
do so, for the world would not hold them.
There is no exception to the nile that every organic being

Chap. III.J GEOMETRICAL RATIO OF INCllE^^SE. 51

naturally increases ut so liigli a rate, that, if not destroyed, the
earth would soon be covered by the progeny of a single pair. Even
slow-breeding man has doubled in twenty-five years, and at this
rate, in less than a thousand years, there would literally not be
standing-room for his progeny. Linna3us has calculated that if an
annual plant produced only two seeds — and there is no plant so
unproductive as this — and their seedlings next year produced two,
and so on, then in twenty years there would be a million plants.
The elephant is reckoned the slowest breeder of all known animals,
and I have taken some pains to estimate its probable minimum rate
of natural increase; it will be safest to assume that it begins
breeding when thirty years old, and goes on breeding till ninety
years old, bringing forth six young in the interval, and surviving
till one hundred years old ; if this be so, after a period of from
740 to 750 years there would be nearly nineteen million elephants
alive, descended from tbe first pair.

But we have better evidence on this subject than mere theoretical
calculations, namely, the numerous recorded cases of the astonish-
ingly rapid increase of various animals in a state of nature, when
circumstances have been favourable to them during Uwo or three
following seasons. Still more striking is the evidence from oi:r
domestic animals of many kinds which have run wild in several
parts of the world ; if the statements of the rate of increase ot
slow-breeding cattle and horses in South America, and latterly
in Australia, had not been well authenticated, they would have
been incredible. So it is with plants; cases could be given of
introduced plants which have become common throughout whole
islands in a period of less than ten years. Several of the plants^
such as the cardoon and a tall thistle, which are now the com-
monest over the wide plains of La Plata, clothing square leagues
of surface almost to the exclusion of every other plant, have been
introduced from Europe ; and there are plants whicli now range in
India, as I hear from Dr. Falconer, from Cape Comorin to the
Himalaya, which have been imported from America since its dis-
covery. In such cases, and endless others could be given, no one
supposes, that the fertility of the animals or plants has been suddenly
and temporarily increased in any sensible degree. The obvious
explanation is that the conditions of life have been highly favourable,
and that there has consequently been less destruction of the old and
voung, and that nearly all the young have been enabled to breedL
*Their geometrical ratio of increase, the result of which never fails to
be surprising, simply explains their extraordinarily rapid increase

d wide diffusion in their new homes.

E 2

52 GEOMETRICAL RATIO OF INCREASE. [Chap. Ill,

In a state of nature almost every full-grown plant annually
produces seed, and amongst animals there are very few which do
not annually pair. Hence we may confidently assert, that all
plants and animals are tending to increase at a geometrical ratio, —
that all would rapidly stock every station in which they could any
how exist, — and that this geometrical tendency to increase must be
checked by destruction at some period of life. Our familiarity with
the larger domestic animals tends, I think, to mislead us : we see
no great destruction falling on them, but we do not keep in mind
that thousands are annually slaughtered for food, and that in a state
of nature an equal number would have somehow to be disposed of.

The only difference between organisms which annually produce
eggs or seeds by the thousand, and those which produce extremely
few, is, that the slow-breeders would require a few more years to
people, under favourable conditions, a whole district, let it be ever
so large. The condor lays a couple of eggs and the ostrich a score,
and yet in the same country the condor may be the more numerous
of the two ; the Fulmar petrel lays but one egg, yet it is believed
to be the most numerous bird in the world. One fly deposits
hundreds of eggs, and another, like the hippobosca, a single one ;
but this difference does not determine how many individuals of the
two species can be supported in a district. A large number of eggs
is of some importance to those species which depend on a fluctua-
ting amount of food, for it allows them rapidly to increase in
number. But the real importance of a large number of eggs or
seeds is to make up for much destruction at some period of life ;
and this period in the great majority of cases is an early one. If
an animal can in any way protect its own eggs or young, a small
number may be produced, and yet the average stock be fully kept
up ; but if many eggs or young are destroyed, many must be
produced, or the species will become extinct. It would suffice to
keep up the full number of a tree, which lived on an average for a
thousand years, if a single seed were produced once in a thousand
years, supposing that this seed were never destroyed, and could be
ensured to germinate in a fitting place. So that, in all cases, the
average number of any animal or plant depends only indirectly on
the number of its eggs or seeds.

In looking at Nature, it is most necessary to keep the foregoing
considerations always in mind — never to forget that every single
organic being may be said to be striving to the utmost to increase
in numbers ; that each lives by a struggle at some period of its life ;
that neavy destruction inevitably falls either on the young or o^d,
during each generation or at recurrent intervals. Lighter ani

CHAP. III. J NATURE OF THE CHECKS TO INCREASE.

63

check, mitigate the destruction ever so little, and the number of
the species will almost instantaneously increase to any amount.

Nature of the Checks to Increase.

The causes which check the natural tendency of each species to
.ncrease are most obscure. Look at the most vigorous species ; by
as much as it swarms in numbers, by so much will it tend to
increase still further. "We know not exactly what the checks are
even in a single instance. Nor will this surprise any one who
reflects how ignorant we are on this head, even in regard to mankind,
although so incomparably better known than any other animal. This
subject of the checks to increase has been ably treated by several
authors, and I hope in a future work to discuss it at considerable
length, moi'e especially in regard to the feral animals of South
America. Here I will make only a few remarks, just to recall to
the reader's mind some of the chief points. Eggs or very young
animals seem generally to suffer most, but this is not invariably the
case. With plants there is a vast destruction of seeds, but, from
some observations which I have made it appears that the seedlings
jsufifer most from germinating in ground already thickly stocked
with other plants. Seedlings, also, are destroyed in vast numbers
by various enemies ; for instance, on a piece of ground three feet
long and two wide, dug and cleared, and where there could be no
choking from other plants, I marked all the seedlings of our native
weeds as they came up, and out of 357 no less than 295, were
destroyed, chiefly by slugs and insects. If turf which has long been
mown, and the case would be the same with turf closely browsed
by quadrupeds, be let to grow, the more vigorous plants gradually
kill the less vigorous, though fully grown plants ; thus out oi
twenty species growing on a little plot of mown turf (three feet by
four) nine species perished, from the other species being allowed to
grow up freely.

The amount of food for each species of course gives the extreme
limit to which each can increase ; but very frequently it is not the
obtaining food, but the serving as prey to other animals, which
determines the average numbers of a species. Thus, there seems to
be little doubt that the stock of partridges, grouse, and hares on
any large estate depends chiefly on the destruction of vermin. If
not one head of game were shot during the next twenty years in
England, and, at the same time, if no vermin were destroyed, there
would, in all probability, be less game than at present, although
hundreds of thousands of game animals are now annually shot. On
the other hand, in some cases, as with the elephant, none are

l^

'>^,

54 NATURE OF THE CHECKS TO INCREASE. [Chap. II!.

destroyed by beasts of prey ; for even the tiger in India mout rarely
dares to attack a young elephant protected by its dam.

Climate plays an important part in determining the average
numbers of a species, and periodical seasons of extreme cold or
drought seem to be the most effective of all checks. I estimated
(chiefly from the greatly reduced numbers of nests in the spring)
that the winter of 1854-5 destroyed four-fifths of the birds in my
own grounds; and this is a tremendous destruction, when we
remember that ten per cent, is an extraordinarily severe mortality
from epidemics with man. The action of climate seems at first
sight to be quite independent of the struggle for existence ; but m
s^o far as climate chiefly acts in reducing food, it brings on the most
severe struggle between the individuals, whether of the same or of
distinct species, which subsist on the same kind of food. Even
when climate, for instance extreme cold, acts directly, it will be
the least vigorous individuals, or those which have got least food
through the advancing winter, which will suffer most. When we
travel from south to north, or from a damp region to a dry, we
mvariably see some species gradually getting rarer and rarer, and
finally disappearing ; and the change of climate being conspicuous,
we are tempted to attribute the whole effect to its direct action.
But this is a false view ; we forget that each species, even where it
most abounds, is constantly suffering enormous destruction at some
period of its life, from enemies or from competitors for the same
place and food ; and if these enemies or competitors be in the least
degree favoured by any slight change of climate, they will increase
in numbers ; and as each area is already fully stocked with inhabi-
tants, the other species must decrease. When we travel south-
ward and see a species decreasing in numbers, we may feel sure
that the cause lies quite as much in other species being favoured, as
in this one being hurt. So it is when we travel northward, but in
a somewhat lesser degree, for the number of species of all kinds,
and therefore of competitors, decreases northwards ; hence in going
northwards, or in ascending a mountain, we far oftener meet with
Btunted forms, due to the directly injurious action of climate, than we
do in proceeding southwards or in descending a mountain. When
we reach the Arctic regions, or snow-capped summits, or absolute
deserts, the struggle for life is almost exclusively with the elements.

That climate acts in main part indirectly by favouring other
species, we clearly see in the prodigious number of plants which
in our gardens can perfectly well endure our climate, but which
never become naturalised, for they cannot compete with our native
plants nor resist destruction by our native animals.

CiiAP. III.3 STRUGGLE FOR EXISTENCE. . 55

When a species, owing to highly favourable circumstances,
increases inordinately in numbers in a small tract, epidemics — at
least, this seems generally to occur with our game animals — often
ensue ; and here we have a limiting check independent of the
struggle for life. But even some of these so-called epidemics
appear to be due to parasitic worms, which have from some cause,
possibly in part through facility of diffusion amongst the crowded
animals, been disproportionally favoured : and here comes in a sort
of struggle between the parasite and its prey.

On the other hand, in many cases, a large stock of individuals
of the same species, relatively to the numbers of its enemies, is
absolutely necessary for its preservation. Thus we can easily raise
Ijlenty of corn and rape-seed, &c., in our fields, because the seeds
are in great excess compared with the number of birds which feed
on them ; nor can the birds, though having a superabundance of
food at this one season, increase in number proportionally to the
bupply of seed, as their numbers are checked during winter; but
any one who has tried, knows how troublesome it is to get seed
from a few v^^heat or other such plants in a garden : I have in thiis*
case lost every single seed. This view of the necessity of a large
stock of the same species for its preservation, explains, I believe,
some singular facts in nature such as that of very rare plants being
sometimes extremely abundant, in the few spots where they do
exist ; and that of some social plants being social, that is abounding
in individuals, even on the extreme verge of their range. For in
such cases, we may believe, that a plant could exist only where the
conditions of its life were so favourable that many could exist
together, and thus save the species from utter destruction. I
should add that the good effects of intercrossing, and the ill effects
of close interbreeding, no doubt come into play in many of theso
cases ; but I will not here enlarge on this subject.

Complex delations of all Animals and Plants to each other tn
the Struggle for Existence,

Many cases are on record showing how complex and unexpected
are the checks and relations between organic beings, which have tc
struggle together in the same country. I will give only a single
instance, which, though a simple one, interested me. In Stafford-
shire, on the estate of a relation, where I had ample means of
investigation, there was a large and extremely barren heath, which
had never been touched by the hand of man ; but several hundred
acres of exactly the same nature had been enclosed twenty-five
years previously and planted with Scotch fir. The change in the

56 STRUGGLE FOR EXISTENCE. [Chap. Ill

Dative vegetation of the planted part of the heath was most
remarkable, more than is generally seen in passing from one quite
different soil to another ; not only the proportional numbers of the
heath-plants were wholly changed, but twelve species of plants (not
■counting grasses and carices) flourished in the plantations, which
could not be founsi on the heath. The effect on the insects must
have been still greater, for six insectivorous birds were very
nommon in the plantations, which were not to be seen on the
neath ; and the heath was frequented by two or three distinct
insectivorous birds. Here we see how potent has been the effect of
the introduction of a single tree, nothing whatever else having been
'done, with the exception of the land having been enclosed, so that
'cattle could not enter. But how important an element enclosure is,
I plainly saw near Farnham, in Surrey. Here there are extensive
heaths, with a few clumps of old Scotch firs on the distant hill-
tops : within the last ten years large spaces have been enclosed,
and self-sown firs are now springing up in multitudes, so close
together tliat all cannot live. When I ascertained that these
young trees had not been sown or planted, I was so much sur-
prised at their numbers that I went to several points of view,
v/hence I could examine hundreds of acres of the unenclosed heath,
and literally I could not see a single Scotch fir, except the old
planted clumps. But on looking closely between the stems of the
heath, I found a multitude of seedlings and little trees which had
been perpetually browsed down by the cattle. In one square yard,
at a point some hundred yards distant from one of the old clumps,
I counted thirty-two little trees ; and one of them, with twenty-
six rings of growth, had, during many years tried to raise its head
above the stems of the heath, and had failed. No wonder that, as
soon as the land was enclosed, it became thickly clothed with
vigorously growing young firs. Yet the heath was so extremely
barren and so extensive that no one would ever have imagined that
cattle would have so closely and effectually searched it for food.

Here we see that cattle absolutely determine the existence of
the Scotch fir ; but in several parts of the world insects determine the
existence of cattle. Perhaps Paraguay offers the most curious
instance of this ; for here neither cattle nor horses nor dogs have
ever run wild, though they swarm southward and northward in a
feral state ; and Azara and Rengger have shown that this is caused
by the greater number in Paraguay of a certain fly, which lays its
^gs in the navels of these animals when first born. The increase
of these flies, numerous as they are, must be habitually checked by
some means, probably by other parasitic insects. Hence, if certain

Chap. III.) STRUGGLE FOR EXISTENCE. 57

insectiTorous birds were to decrease in Faragiia}', the parasitic
insects would probably increase ; and this would lessen the number
of the navel-frequenting flies — then cattle and horses would become
feral, and this would certainly greatly alter (as indeed I have obser-
ved in parts of South America) the vegetation : this again would
largely affect the insects; and this, as we have just seen in Stafford-
shire, the insectivorous birds, and so onwards in ever-increasing
circles of complexity. Not that under nature the relations will
ever be as simple as this. Battle within battle must be con-
tinually recurring with varying success ; and yet in the long-
run the forces are so nicely balanced, that the face of nature remains
for long periods of time uniform, though assuredly the merest trifle
would give the victory to one organic being over another. Never-
theless, so profound is our ignorance, and so high our presumption,
that we marvel when we hear of the extinction of an organic being ;
and as we do not see the cause, we invoke cataclysms to desolate the
world, or invent laws on the duration of the forms of life !

I am tempted to give one more instance showing how plants and
animals, remote in the scale of nature, are bound together by a web
of complex relations. I shall hereafter have occasion to show thai
the exotic Lobelia fulgens is never visited in my garden by insects,
and consequently, from its peculiar structure, never sets a seed.
Nearly all our orchidaceous plants absolutely require the visits of
insects to remove their pollen-masses and thus to fertilise them. I
find from experiments that humble-bees are almost indispensable to
the fertilisation of the heartsease (Viola tricolor), for other bees do
not visit this flower. I have also found that the visits of bees are
necessary for the fertilisation of some kinds of clover : for instance?
20 heads of Dutch clover (Trifolium repens) yielded 2,290 seeds, but
20 other heads protected from bees produced not one. Again, 100
heads of red clover (T. pl-aTen'S'e) producedr-^TTOCTseeds^ but the same
number of protected beads produced not a single seed. Humble-bees
alone visit red clover, as other bees cannot reach the nectar. It has
been suggested that moths may fertilise the clovers ; but I doubt
whether they could do so in the case of the red clover, from their
weight not being sufficient to depress the wing-petals. Hence we
may infer as highly probable that, if the whole genus of humble-bees
became extinct or very rare in England, the heartsease and red
clover would become very rare, or wholly disappear. The number
of humble-bees in any district depends in a great measure on the
number of field-mice, which destroy their combs and nests ; and
CoL Newman, who has long attended to the hab:Us of humble-bees,

58 STRUGGLE FOR EXISTENCE. [Chap. IIL

believes that " more than two-thirds of them are thus destroyed all
over England." Now the number of mice is largely dependent, aa
every one knows, on the number of cats ; and Col. Newman says,
" Near villages and small towns I have found the nests of humble-
bees more numerous than elsewhere, which I attribute to the num-
ber of cats that destroy the mice." Hence it is quite credible that
the presence of a feline animal in large numbers in a district might
determine, through the intervention first of mice and then of bees,
the frequency of certain flowers in that district !

In the case of every species, many different checks, acting at
different periods of life, and during different seasons or years, pro-
bably come into play ; some ons check or some few being generally
the most potent ; but all will concur in determining the average
number or even the existence of the species. In some cases it can
be shown that widely-different checks act on. the same species
in different districts. When we look 2.t the plants and bushes
clothing an entangled bank, we are tempted to attribute their pro-
portional numbers and kinds to what we call chance. But how false
a view is this ! Every one has heard that when an American forest
is cut down, a very different vegetation springs up ; but it has been
observed that ancient Indian ruins in the Southern United States,
which must formerly have been cleared of trees, now display the
same beautiful diversity and proportion of kinds as in the surround-
ing virgin forest. What a struggle must have gone on during long
centuries between the several kinds of trees, each annually scattering
its seeds by the thousand ; what war between insect and insect —
between insects, snails, and other animals with birds and beasts of
prey — all striving to increase, all feeding on each other, or on the
trees, their seeds and seedlings, or on the other plants which first
clothed the ground and thus checked the growth of the trees ! Throw
up a handful of feathers, and all fall to the ground according to
definite laws ; but how simple is the problem where each shall fall
compared to that of the action and reaction of the innumerable
plants and animals which have determined, in the course of cen-
turies, the proportional numbers and kinds of trees now growing on
the old Indian ruins !

The dependency of one organic being on another, as of a parasite
on its prey, lies generally between beings remote in the scale of
nature. This is likewise sometimes the case with those which may
be strictly said to struggle with each other for existence, as in the
case of locusts and grass-feeding quadrupeds. But the struggle will
almost invariably be most severe between the individuals of the
same species, for they frequent the same districts, require the same

Chap. III.] STRUGGLE FOR EXISTENCE. 5i)

food, and ojio^vpngpt^ fp {f^ ""^"^Q finrpi"^^'" — In the case ot varieties
-t5nKe''*same si^ecies, the struggle will generally be almost equally
severe, and we sometimes see the contest soon decided : for instance,
if several varieties of wheat 1>3 sown together, and tlie mixed seed be
resown, some of the varieties which best suit the soil or climate, or are
naturally the most fertile, will beat the others and so yield more
seed, and will consequently in a few years supplant the other varie-
ties. To keep up a mixed stock of even such extremely close varie-
ties as the variously-coloured sweet-peas, they must be each year
harvested separately, and the seed then mixed in due proportion,
otherwise the weaker kinds will steadily decrease in number and
disappear. So again with the varieties of sheep : it has been asserted
that certain mountain-varieties will starve out other mountain-
varieties, so that they cannot be kept together. The same result
has followed from keeping together different varieties of the medicinal
leech. It may even be doubted whether the varieties of any of oui
domestic plants or animals have so exactly the same strength,
habits, and constitution, that the original proportions cf a mixed
stock (crossing being prevented) could be kept up for half-a-dozen
generations, if they were allowed to struggle together, in the same
manner as beings in a state of nature, and if the seed or young were
not annually preserved in due proportion.

Struggle for Life most severe 'between Individuals and Varieties
of the same Species.

As the species of the same genus usually have, though by no
means invariably, much similarity in habits and constitution, and
always in structure, the struggle will generally be more severe
betv/een them, if they come into competition with each other, than
between the species of distinct genera. We see this in the recent
extension over parts of the United States of one species of swallow
having caused the decrease of another species. The recent increase
of the missel-thrush in narts of Scotland has caused the decrease of
the song-thrush. How frequently we hear of one species of rat
taking the place of another species under the most different climates !
In Kussia the small Asiatic cockroach has everywhere driven before
It its great congener. In Australia the imported hive-bee is rapidly
exterminating the small, stingless native bee. One species of char-
lock has been known to supplant another species ; and so in other
cases. We can dimly see why the competition should be most severe
between allied forms, which fill nearly the same place in the economy
of nature ; but probably in no one case could we precisely say why
one species has been victorious over another in the great battle of lifo,

60 STRUGGLE FOR EXISTENCE. [Chap. 111.

A corollary of the highest importance may be deduced from the
foregoing remarks, namely, that the structure of every organic being
is related, in the most essential yet often hidden manner, to that of
all the other organic beings, with which it comes into competition
for food or residence, or from which it has to escape, or on which it
preys. This is obvious in the structure of the teeth and talons of
the tiger ; and in that of the legs and claws of the parasite which
clings to the hair on the tiger's body. But in the beautifully plumed
(seed of the dandelion, and in the flattened and fringed legs of the
water-beetle, the relation seems at first confined to the elements of
air and water. Yet the advantage of plumed seeds no doubt stands
in the closest relation to the land being already thickly clothed with
other plants ; so that the seeds may be widely distributed and fall
on unoccupied ground. In the water-beetle, the structure of its
legs, so well adapted for diving, allows it to compete with other
aquatic insects, to hunt for its own prey, and to escape serving as
prey to other animals.

The store of nutriment laid up within the seeds of many plants
Beams at first sight to have no sort of relation to other plants. But
from the strong growth of young plants produced from such seeds*
as peas and beans, when sown in the midst of long grass, it may bo
suspected that the chief use of the nutriment in the seed is to favour
the growth of the seedlings, whilst struggling with other plants
growing vigorously all around.

Look at a plant in the midst of its range, why does it not double
or quadruple its numbers? We know that it can perfectly well
withstand a little more heat or cold, dampness or dryness, for else-
where it ranges into slightly hotter or colder, damper or drier dis-
tricts. In this case we can clearly see that if we wish in imagination
to give the plant the power of increasing in number, we should have
to give it some advantage over its competitors, or over the animals
which prey on it. On the confines of its geographical range, a change
of constitution with respect to climate would clearly be an advantage
to our plant ; but we have reason to believe that o^nlv a few plants
or animals range so far, that they are destroyed exclusively by the
rigour of the climate. Not until we reach the extreme confines of
life, in the Arctic regions or on the borders of an utter desert, will
competition cease. The land may be extremely cold or dry, yet
there will be competition between some few species, or between the
individuals of the same species, for the warmest or dampest spots.

Hence we can see that when a plant or animal is placed in a new
country amongst new competitors, the conditions of its life will
generally be changed in an essential manner, although the climate

ty'UAP. III.]

f CE. ^ ITS ^ '

STRUGGLE FOR EXISTENCE.

may be exactlly the same as in its former home. If its average num-
bers are to iniprease in its new home, we should have to modify it in
a different way to what we should have had to do in its native
country ; for we should have to give it some advantage over a different
set of competitors or enemies.

It is good thus to try in imagination to give to any one species an
advantage over another. Probably in no single instance should we
know what to do. This ought to convince us of oiu: ignorance on
the mutual relations of all organic beings ; a conviction as necessary,
as it is difficult to acquire. All that we can do, is to keep steadily
in mind that each organic being is striving to increase in a geometri-
cal ratio ; that each at some period of its life, during some season of
the year, during each generation or at intervals, has to struggle for
life and to suffer great destruction. When we reflect on this strugglej
we may console ourstlves with the full belief, that the war of nature
is not incessant, that no fear is felt, that death is generally prompt,,
and that the vigorous, the healthy, and the happy survive and

1

multiplr

rv\'4.-.''PL-H^X4!^^

62 NATURAL SELECTION. [Ciiap. IV

CHAPTEE IV.

Natural SrLECTioN; or the Survival op ^/he Fittest.

Natural Selection — its power compared with man's selection — its power
on characters of trifling importance — its power at /all ages and on both
sexes — Sexual Selection — On the generality of /intercrosses between
individuals of the same species — Circumstances i favourable and unfa-
vourable to the results of Natural Selection, /lamely, intercrossing,
isolation, number of individuals — Slow action -A Extinction caused by
Natural Selection — Divergence of Character, roilated to the diversity of
inhabitants of any small area, and to naturalisation — Action of Natural
Selection, through Divergence of Character, and Extinction, on the de-
scendants from a common parent — Explains the grouping of all organic
beings — Advance in organisation — Low forms preserved — Convergence
of character — Indefinite multiplication of species — Summary.

How will the struggle for existence, briefly discussed in the last
chapter, act in regard to variation ? Can the principle of selection,
v/hich we have seen is so potent in the hands of man, apply under
nature ? I think we shall see that it can act most efficiently. Let
the endless number of slight variations and individual differences
occurring in our domestic productions, and, in a lesser degree, in
those under nature, be borne in mind ; as well as the strength of
the hereditary tendency. Under domestication, it may be truly
said that the whole organisation becomes in some degree plastic.
But the variability, which we almost universally meet with in our
domestic productions, is not directly produced, as Hooker and
Asa Gray have well remarked, by man ; he can neither originate
varieties, nor prevent their occurrence ; he can only preserve and
accumulate such as do occur. Unintentionally he exposes organic
beings to new and changing conditions of life, and variability
ensues ; but similar changes of conditions might and do occur under
nature. Let it also be borne in mind how infinitely complex and
close-fitting are the mutual relations of all organic beings to each
other and to their physical conditions of life; and consequently
what infinitely varied diversities of structure might be of use to
each being under changing conditions of life. Can it, then, be
thought improbable, se^-ing that variations useful to man have

CUAP. IV.] NATURAL SELECTION. 63

r undoubtedly occurrod, that other variations usetal in some way to

I each being in the great and complex battle of life, should occur in

the course of many successive generations ? If such do occur, can we

doubt (remembering that many more individuals *are born than can

. possibly survive) that individuals having any advantage, however

1 slight, over others, would have the best chance of surviving and of

i procreating their kind ? On the other hand, we may feel sure that

any variation in the least degree injurious would bo rigidly de-

i stroyed. This preservation of favourable individual differences and

J variations, and the destruction of those which are injurious, I have
called Natural Selection, or the Survival of the Fittest. Variations
neither useful nor injurious would not be affected by natural selec-
tion, and would be left either a fluctuating element, as perhaps we
see in certain polymorphic species, or would ultimately become
fixed, owing to the nature of the organism and the nature of the
conditions.

Several writers have misapprehended or objected to the term
Natural Selection. Some have even imagined that natural selection
induces variability, whereas it implies only the preservation of such
variations as arise and are beneficial to the being under its con-
ditions of life. No one objects to agriculturists speaking of the
potent effects of man's selection ; and in this case the individual
differences given by nature, which man for some object selects,
must of necessity first occur. Others have objected that the term
selection iinplies conscious choice in the animals which become
modified; and it has even been urged that, as plants have no voli-
tion, natural selection is not applicable to them! In the literal
sense of the word, no doubt, natural selection is a false term ; but
who ever objected to chemists speaking of the elective affinities of
the various elements ? — and yet an acid cannot strictly be said to
elect the base with which it in preference combines. It has been
said that I speak of natural selection as an active power or Deity ;
but who objects to an author speaking of the attraction of gravity
as ruling the movements of the planets ? Every one knows what
is meant and is implied by such metaphorical expressions ; and
they are almost necessary for brevity. So again it is difficult to
avoid personifying the word Nature ; but I mean by Nature, only
the aggregjatangtion and productof many natural laws, and by lawg
the seq uenci^-aLe vents as ascer tamed byiTs. W ith a little tamiliarify
iuch superficial objections wilTnbe forgotten.

We shall best understand the probable course of natural selection
by taking the case of a country undergoing some slight physical
change, for instance, of climate. The proportional numbers of its

64 NATURAL SELECTION. [Chap. IV,

inhabitants will almost immediately undergo a change, and some
species will probably become extinct. We may conclude, from
what we have seen of the intimate and complex manner in which
the inhabitants of each country are bound together, that any change
in the numerical proportions of the inhabitants, independently of
the change of climate itself, would seriously affect the others. If
the country were open on its borders, new forms would certainly
immigrate, and this would likewise seriously disturb the relations
of some of the former inhabitants. Let it be remembered how
powerful the influence of a single introduced tree or mammal has
been shown to be. But in the case of an island, or of a country
partly surrounded by barriers, into which new and better adapted
forms could not freely enter, we should then have places in the
economy of nature which would assuredly be better filled up, if
some of the original inhabitants were in some manner modified *
for, had the area been open to immigration, these same places would
have been seized on by intruders. In such cases, slight modifica-
tions, which in any way favoured the ii^iividuals of any species, by
better adapting them to their altered conditions, would tend to be
preserved ; and natural selection would have free scope for the work
of improvement.

We have good reason to believe, as -shown in the first-^^ha^t^,
that changes in the conditions of life give a tendency to increased
variability ; and in the foregoing cases the conditions have changed,
and this would manifestly be favourable to natural selection, by
affording a better chance of the occurrence of profitable variations.
Unless such occur, natural selection can do nothing. Under the
term of " variations," it must never be forgotten that mere indivi-
dual difi'erences are included. As man can produce a great result
with his domestic animals and plants by adding up in any given
direction individual differences, so could natural selection, but far
more easily, from having incomparably longer tim.e for action. Nor
do I believe that any great physical change, as of climate, or any un-
usual degree of isolation to check immigration, is necessary in order
that new and unoccupied places should be left, for natural selec-
tion to fill up by improving some of the varying inhabitants. For
as all the inhabitants of each country are struggling together with
nicely balanced forces, extremely slight modifications in the struc-
ture or habits of one species would often give it an advantage over
others ; and still further modifications of the same kind would often
still further increase the advantage, as long as the species continued
Tinder the same conditions of life and profited by similar means of
subsistence and defence. No country can be named in which all

Chap. IV.]

NATURAL SELECTION.

66

the Dative inhabitants are now so perfectly adapted to each otiiei.
and to the physical conditions under which they live, that none of
them could be still better adapted or im]-)roved ; for in all countries,
the natives have been so far conquered by naturalised productions,
that they have allowed some foreigners to take firm possession of
the land. And as foreigners have thus in every country beaten
feK)me of the natives, we may safely conclude that the natives might
have been modified with advantage, so as to have better resisted the
intruders.

As man can producf^, and certainly has produced, a great result
by his methodical and unconscious means of selection, what may not
natural selection effect ? Man can act only on external and visible
characters : Kature, if I may be allowed to personify the natural
preservation or survival of the fittest, cares nothing for appearances,
except in so far as they are useful to any being. She can act on
every internal organ, on every shade of constitutional difference,
on the whole machinery of life. Man selects only for his own
good : Nature only for that of the being which she tends. Every
selected character is fully exercised by her, as is implied by the fact
of their selection.'^ Man keejis the natives of many climates in the
same country ; he seldom exercises each selected character in some
peculiar and fitting manner ; he feeds a long and a short beaked
pigeon on the same food; he docs not exercise a long-backed or
long-legged quadruped in any peculiar manner ; he exposes sheep
with long and short wool to the same climate. He does not allow
the most vigorous males to struggle for the females. He does not
rigidly destroy all inferior animals, but protects during each varying
season, as far as lies in his power, all his productions. He often
begins his selection by some half-monstrous form ; or at least by
some modification prominent enough to catch the eye or to be
plainly useful to him. Under nature, the slightest differences of
structure or constitution may well turn the nicely-balanced scale in
the struggle for life, and so be preserved. How fleeting are thft ife-tVc "j^
wishes and efforts of man ! how short his time ! and consequently
h'ow~poor will be his results, compared with those .accumulated by
Ijatufe ddring whole geologi^caTperioHi"! Can we wonder, then, that ,'
Nature's productions shculd be far "Truer" in character than man's
productions ; that they should be infinitely better adapted to the
most complex conditions of life, and shoiild plainly bear the stamp
of far higher workmanship ?

It may metaphorically be said that natural selection is daily and'
hourly scrutinising, throughout the world, the slightest variations ;
rejecting those that are bad, preserving and adding up all that ano

- — " Y

6Q NATURAL SELECTION. [Chap. IV

good ; silently and insensibly working, wlienever ami loherevtr
opportunity offers^ at the improvement ofeacli organic Toeing in
fetalTon to its organic and inorganic conditions of life. We see
nothing of these slow changes in progress, until the hand of time
tias- marked the lapse of ages, and then so imperfect is our view into
long-past geological ages, that we see only that the forms of life are
ow different from what they formerly were.

In order that any great amount of modification should be effected
in a species, a variety when once formed must again, perhaps after
a long interval of time, vary or present individual differences of the
same favourable nature as before ; and these must be again pre-
served, and so onwards step by step. Seeing that individual
differences of the same kind perpetually recur, this can hardly be
considered as an unwarrantable assumption. But whether it is
true, we can judge only by seeing how far the hypothesis accords
with and explains the general phenomena of nature. On the other
hand, the ordinary belief that the amount of possible variation is a
strictly limited quantity is likewise a simple assumption.

Although natural selection can act only through and for the good
of each being, yet characters and structures, which we are apt to
consider as of very trifling importance, may thus be acted on. When
we see leaf-eating insects green, and bark-feeders mottled-grey; the
alpine ptarmigan white in winter, the red-grouse the colour of
heather, we must believe that these tints are of service to these
birds and insects in preserving them from danger. Grouse, if not
destroyed at some period of their lives, would increase in countless
numbers ; they are known to suffer largely from birds of prey ; and
hawks are guided by eyesight to their prey — so much, so, that on
parts of the Continent persons are warned not to keep white
pigeons, as being the most liable to destruction. Hence natural
selection might be effective in giving the proper colour to each
kind of grouse, and in keeping that colour, when, once acquired,
true and constant. Nor ought we to think that the occasional
destruction of an animal of any particular colour would produce
little effect : we should remember how essential it is in a flock of
white sheep to destroy a lamb with the faintest trace of black.
We have seen how the colour of the hogs, which feed on the
" paint-root " in Yirginia, determines whether they shall live or die.
In plants, the down on the fruit and the colour of the flesh are con-
sidered by botanists as characters of the most trifling importance :
yet we hear from an excellent horticulturist. Downing, that in the
United States smooth-skinned fruits suffer far more from a beetle,
a Curculio, than those with down ; that purple plums suffer fa;

CnAP. IV.] NATURAL SELECTION. 67

more Ci-om a certain disease than yellow plums ; whereas another
disease attacks yellow-fieshcd peaches far more than those with
other coloured flesh. If, with all the aids of art, these slight differ-
ences make a great difference in cultivating the several varieties,
assuredly, in a state of nature, where the trees would have to
struggle with other trees and with a host of enemies, such differ-
ences would effectually settle which variety, whether a smooth or
downy, a yellow or purple fleshed fruit, should succeed.

In looking at many small points of difference between species,
which, as far as our ignorance permits us to judge, seem quite
unimportant, we must not forget that climate, food, &c., have no
doubt produced some direct effect. It is also necessary to bear in
mind that, owing to the law of correlation, when one part varies,
and the variations are accumulated through natural selection, other
modifications, often of the most unexpected nature, will ensue.

As we see that those variations which, under domestication appear
at any particular period of life, tend to reappear in the offspring at
the same period ; — for instance, in the shape, size, and flavour of
the seeds of the many varieties of our culinary and agricultural
plants ; in the caterpillar and cocoon stages of the varieties of the
silkworm ; in the eggs of poultry, and in the colour of the down of
their chickens ; in the horns of our sheep and cattle when nearly
adult ; — so in a state of nature, natural selection will be enabled to
act on and modify orgaiuc beings at any age, by the accumulation
of variations profitable at that age, and by their inheritance at a
corresponding age. If it profit a plant to have its seeds more and
more widely disseminated by the wind, I can see no greater diffi-
culty in this being effected through natural selection, than in the
cotton-planter increasing and improving by selection the down in
the pods on his cotton-trees. Natural selection may modify and
adapt the larva of an insect to a score of contingencies, wholly
different from those which concern the mature insect ; and these
modifications may affect, through correlation, the structure of the
adult. So, conversely, modifications in the adult may affect
the structure of the larva ; but in all cases natural selection will
ensure that they shall not be injurious: for if they were so, the-
species would become extinct.

^~^aLaial selucLiou vvUlrmodify the structure of the young in relation
to the parent, and of the parent in relation to the young. In social
animals it will adapt the structure of each individual for the benefit,
of the whole community ; if the community profits by the selected
change. What natural selection cannot do, is to modify the struc-
ture of one species, without giving it any advantage, for the goc<l of

F i2

-^8 NATURAL SELECTION. [Chap. IV.

another species ; and though statements to this efifect may be found
in works of natural history, I cnnnot find one case which will bear
investigation. A structure used only once in an animal's life, if of
high importance to it, might be modified to any extent by natural
selection ; for instance, the great jaws possessed by certain insects,
used exclusively for opening the cocoon — or the hard tip to the
beak of unhatched birds, used for breaking the egg. It has been
asserted, that of the best short-beaked tumbler-pigeons a greater
number perish in the egg than are able to get out of it ; so that
fanciers assist in the act of hatching. Now if nature had to make
the beak of a full-grown pigeon very short for the bird's own advan-
tage, the process of modification would be very slow, and there
would be simultaneously the most rigorous selection of all the
young birds within the egg, which had the most powerful and
hardest beaks, for all with weak beaks would inevitably perish ; or,
more delicate and more easily broken shells might be selected,
the thickness of the shell being known to vary like every other
structure.

It may be well here to remark that with all beings there must be
much fortuitous destruction, which can have little or no influence
on the course of natural selection. For instance a vast number of
eggs or seeds are annually devoured, and these could be modified
through natural selection only if they varied in some manner which
protected them from their enemies. Yet many of these eggs or
seeds would perhaps, if not destroyed, have yielded individuals
better adapted to their conditions of life than any of those which
happened to survive. So again a vast number of mature animalfi
and plants, whether or not they be the best adapted to their con-
ditions, must be annually destroyed by accidental causes, which
would not be in the least degree mitigated by certain changes of
structure or constitution which would in other ways be beneficial to
the species. But let the destruction of the adults be ever so heavy,
if the number which can exist in any district be not wholly kept
down by such causes, — or again let the destruction of eggs or seeds
be so great that only a hundredth or a thousandth part are developed,
— yet of those which do survive, the best adapted individuals, sup-
posing that there is any variability in a favourable direction, will
tend to propagate their kind in larger numbers than the less well
adapted. If the numbers be whoUj kept down by the causes just
indicated, as will often have been the case, natural selection will be
powerless in certain beneficial directions ; but this is no valid
objection to its efficiency at other times and in other ways ; for wo
01*6 far from ha^-ing any reason to suppose that many species ever

Chap. IV.] SEXUAL SELECTION. 69

undergo modification and improvement at the same time in the
same area.

Sexual Selection.

Inasmuch as peculiarities often appear under domestication in one
PCX and become hereditarily attached to that sex, so no doubt it aviU
be under nature. Thus it is rendered possible for the two sexes to
be modified through natural selection in relation to different habits
of life, as is sometimes the case ; or for one sex to be mod' 5ed in
relation to the other sex, as commonly occurs. This lead? me to
say a few words on what I have called Sexual Selection. This form of
selection depends, not on a struggle for existence in relation to other
organic beings or to external conditions, but on a struggle between
the individuals of one sex, generally the males, for the possession of
the other sex. The result is not death to the unsuccessful com-
petitor, but few or no offspring. Sexual selection is, therefore, less
rigorous than natural selection. Generally, the most vigorous males,
those which are best fitted for their places in nature, will leave most
progeny. But in many cases, victory depends not so much on
general vigour, as on having special weapons, confined to the male
sex. A hornless stag or spurless cock would have a poor chance of
leaving numerous ofispring. Sexual selection, by always allowing
the victor to breed might surely give indomitable courage, length
to the spur, and strength to the wing to strike in the spurred leg, in
nearly the same manner as does the brutal cockfighter by the care-
ful selection of his best cocks. How low in the scale of nature the
law of battle descends, I know not ; male alligators have been
described as fighting, bellou'ing, and whirling round, like Indians in
a war-dance, for the possession of the females ; male salmons have
been observed fighting all day long ; male stag-beetles sometimes
bear wounds from the huge mandibles of other males ; the males
of certain hymenopterous insects have been frequently seen by that
inimitable observer M. Fabre, fighting for a particular female who
sits by, an apparently unconcerned beholder of the struggle, and
then retires with the conqueror. The war is, perhaps, severest
between the males of polygamous animals, and these seem oftenest
provided with special weapons. Tho males of carnivorous animals
are already well armed; though to them and to others, special
means of defence may be given through means of sexual selection,
as the mane to the lion, and the hooked jaw to the male salmon ;
for the shield may be as important for victory, as the sword or
8pear.

Amongst birds, the contest is often of a more peaceful charactex^

70 SEXUAL SELECTTOX. [Chap. IV.

All those who have attended to the subject, believe that there is the
severest rivalry between the males of many species to attract, by
singing, the females. The rock-thrush of Guiana, birds of paradise, and
some others, congregate ; and successive males display with the most
elaborate care, and show off in the best manner their gorgeous plu-
mage; they likewise perform strange antics before the females, which,
standing by as spectators, at last choose the most attractive partner.
Those who have closely attended to birds in confinement well know
that they often take individual preferences and dislikes; thus Sir E,
Heron has described how a pied peacock was eminently attractive to
all his hen birds. I cannot Jiere enter on the necessary details ; but
if man can in a short time give beauty and an elegant carriage to his
bantams, according to his standard of beauty, I can see no good
reason to doubt that female birds, by selecting, during thousands of
generations, the most melodious or beautiful males, according to their
standard of beauty, might produce a marked effect. Some well-
known laws, with respect to the plumage of male and fernale birds,^
in comparison with the plumage of the young, can partly be ex-
plained through the action of sexual selection on variations occurring
at different ages, and transmitted to the males alone or to both sexes
at corresponding ages ; but I have not space here to enter on this
subject.

Thus it is, as I believe, that when the males and females of any
animal have the same general habits of life, but differ in structure,
colour, or ornament, such differences have been mainly caused by
sexual selection : that is, by individual males having had, in suc-
cessive generations, some slight advantage over other males, in their
weapons, means of defence, or charms, which they have transmitted
to their male offspring alone. Yet, I would not wish to attribute all
sexual differences to this agency : for we see in our domestic animals
peculiarities arising and becoming attached to the male sex, which
apparently have not been augmented through selection by man.
The tuft of hair on the breast of the wild turkey-cock cannot be of
any use, and it is doubtful whether it can be ornamental in the eyes
of the female bird ; — indeed, had the tuft appeared under domestica-
tion, it would have bsen called a monstrosity.

Illustrations of the Action of Natural Selection^ or the Survival

of the Fittest,

In order to make it clear how, as I believe, natural selection acts,
I must beg permission to give one or two imaginary illustrations.
Let us take the case of a wolf, which preys on various animals,
securing some by craft, some by strength, and some by fleetness j

Chap. IV.] NATURAL SELECTION. 71

and let us suppose that the fleetest prey, a deer for instance, bad
from any change in the country increased in numbers, or that other
prey had decreased in numbers, during that season of the year when
the wolf was hardest pressed for food. Under such circumstances the
swiftest and slimmest wolves would have the best chance of surviv-
ing, and so be preserved or selected, — provided always that they
retained strength to master their prey at this or some other period of
the year, when they were compelled to prey on other animals. I can
see no more reason to doubt that this would be the result, than that
man should be able to improve the fleetuess of his greyhouuds by
careful and methodical selection, or by that kind of unconscious
selection which follows from each man trying to keep the best dogs
without any thought of modifying the breed. I may add, that,
according to Mr. Pierce, there are two varieties of the wolf inhabiting
the Catskill Mountains in the Uriited States, one with a light grey-
hound-like form, which pursues deer, and the other more bulky,
with shorter legs, which more frequently attacks the shepherd's
flocks.

It should be observed that, in the above illustration, I speak of
the slimmest individual wolves, and not of ariy single strongly-
marked variation iiaving been preserved. In former editions of ttis
work I sometimes spoke as if this latter alternative had frequently
occurred. I saw the great importance of individual differences, and
this led me fully to discuss the results of unconscious selection by
man, which depends on the preservation of all the more or less
valuable individuals, and on the destruction of the worst. I saw,
also, that the preservation in a state of nature of any occasional
deviation of structure, such as a monstrosity, would be a rare event ;
and that, if at first preserved, it would generally be lost by subse-
quent intercrossing v/ith ordinary individuals. Nevertheless, until
reading an able and valuable article in the ' North British Eeview '
(1867), I did not appreciate how rarely single variations, whether
slight or strongly-marked, could be perpetuated. The author takes
the case of a pair of animals, producing during their lifetime two
hundred offspring, of which, from various causes of destruction, only
two on an average survive to pro-create their kind. This is rather
an extreme estimate for most of the higheranimals, butby nomeans
so for many of the lower organisms. He then shows that if a single
individual were born, which varied in some manner, giving it twice
as good a chance of life as that of the other individuals, j'ct the
chances would be stiongly against its survival. Supposing it to
tjurvive and to breed, and that half its young inherited the favour-
able variation ; still, as the Keviewer goes on to show, the young

72 ILLUSTRATIONS OF THE ACTION OF [Chap. IV

would have only a slightly better chance of surviving and bre(3dingi
and tins chance would go on decreasing in the succeeding genera-
tions. The justice of these remarks cannot, I think, be disputed.
if, for instance, a bird of some kind could procure its food more
easily by having its beak curved, and if one were born with its beak
strongly curved, and which consequently flourished, nevertheless
there would be a very poor chance of this one individual perpetuat-
ing its kind to the exclusion of the common form ; but there can
hardly be a doubt, judging by what we see taking place under
domestication, that this result would follow from the preservation
during many generations of a large number of individuals with more
or less strongly curved beaks, and from the destruction of a still
larger number with the straightest beaks.

^/'Urshould not, however, be overlooked that certain rather strongly
'marked variations, which no one would rank as mere individual
differences, frequently recur owing to a similar organisation being
similarly acted on, — of which fact numerous instances could be
given with our domestic productions. In such cases, if the varj'ing
individual did not actually transmit to its offspring its newly-acquired
character, it would undoubtedly transmit to them, as long as the
existing conditions remained the same, a still stronger tendency to
vary in the same manner. There can also be little doubt that the
tendency to vary in the same manner has often been so strong that
all the individuals of the same species have been similarly modified
without the aid of any form of selection. Or only a third, fifth, or
tenth part of the individuals may have been thus affected, of which
fact several instances could be given. Thus Graba estimates that
about one-fifth of the guillemots in the Faroe Islands consist of a
variety so well marked, tli^t it was formerly ranked as a distinct
species under the name of Uria lacrymans. In cases of this kind, if
the variation were of a beneficial nature, the original form would
soon be supplanted by the modified form, through the survival of
the fittest.

To the effects of intercrossing in eliminating variations of all
kinds, I shall have to recur ; but it may be here remarked that
most animals and plants keep to their proper homes, and do
not needlessly wander about ; we see this even with migratory
birds, which almost always return to the same spot. Consequently
each newly-formed variety would generally be at first local, as seems
to be the common rule with varieties in a state of nature ; so that
similarly modified individuals would soon exist in a small body
together, and would often breed together. If the new variety were
successful in its battle for life, it would slowly spread from a centra)

CuAP. I V.J NATURAL SELECTION. 73

district, competing with and conquering the unchanged individuals
on the margins of an ever-increasiag circle.

It may be worth while to give another and more complex illus-
tration of the action of natural selection. Certain plants excrete
sweet juice, apparently for the sake of eliminating something in-
jurious from the sap : this is effected, for instance, by glands at the
base of the stipules in some Leguminosa3, and at the backs of the
leaves of the common laurel. This juice, though small in quantity _,
is greedily sought by insects ; but their visits do not in any way
benefit the plant. Now, let us suppose that the juice or nectar was
excreted from the inside of the flowers of a certain number of plants
of any species. Insects in seeking the nectar would get dusted with
pollen, and would often transport it from one flower to another.
The flowers of two distinct individuals of the same species would
thus get crossed ; and the act of crossing, as can be fully proved,
gives rise to vigorous seedlings, which consequently would have the
best chance of flourishing and surviving. The plants which produced
flowers with the largest glands or nectaries, excreting most nectar,
would oftenest be visited by insects, and would oftenest be crossed ;
and so in the long-run would gain the upper hand and form a local
variety. The flowers, also, which had their stamens and pistils
placed, in relation to the size and habits of the particular insect
which visited them, so as to favour in any degree the transportal of
the pollen, would likewise be favoured. We might have taken the
case of insects visiting flowers for the sake of collecting pollen in-
stead of nectar; and as pollen is formed for the sole purpose of
fertilisation, its destruction appears to be a simple loss to the plant ;
yet if a little pollen were carried, at flrst occasionally and then
habitually, by the pollen-devouring insects from flower to flower,
and a cross thus effected, although nine-tenths of the pollen were
destroyed, it might still be a great gain to the plant to be thus
robbed ; and the individuals which produced more and more pollen,
and had larger anthers, would be selected.

When our plant, by the above process long continued, had been
rendered highly attractive to insects, they would, unintentionally on
their part, regularly carry pollen from flower to flower ; and that
they do this effectually, I could easily show by many striking facts.
I will give only one, as likewise illustrating one step in the separa-
tion of the sexes of plants. Some hoily-trees bear only male flowers,
which have four stamens producing a rather small quantity of
pollen, and a rudimentary pistil ; other holly-trees bear only female
flowers; these have a full-sized pistil, and four stamens witli
shrivelled anthers, in which not a grain of pollen can be detected

74 ILLUSTRATIONS OF THE ACTION OF [Chap. IV.

IlaTiDg found a female tree exactly sixty yards from a male tree.. 1
put the stigmas of twenty flowers, taken from different branches,
under the microscope, and on all, without exception, there were a
few pollen-grains, and on some a profusion. As the wind had set
for several days from the femaLe to the male tree, the pollen could
not thus have been carried. The weather had been cold and
boisterous, and therefore not favourable to bees, nevertheless every
female flower which I examined had been effectually fertilised by
the bees, which had flown from tree to tree in search of nectar. But
to return to our imaginary case : as soon as the plant had been
rendered so highly attractive to insects that pollen was regularly
carried from flower to flower, another process might commence. No
naturalist doubts the advantage of what has been called the "physio-
logical division of labour ; " hence we may believe that it would be
advantageous to a plant to produce stamens alone in one flower or
on one whole plant, and pistils alone m another flower or on another
plant. In plants under culture and placed under new conditions of
life, sometimes the male organs and sometimes the female organs
become more or less impotent ; now if we suppose this to occur in
ever so slight a degree under nature, then, as pollen is already
carried regularly from flower to flower, and as a more complete sepa-
ration of the sexes of our plant would be advantageous on the prin-
ciple of the division of labour, individuals with this tendency more
and more increased, would be continually favoured or selected,
until at last a complete separation of the sexes might be effected.
It would take up too much space to show the various steps,
through dimorphism and other means, by which the separation of
the sexes in plants of various kinds is apparently now in progress ;
but I may add that some of the species of holly in North America,
are, according to Asa Gray, in an exactly intermediate condition, or,
as he expresses it, are more or less dioeciously polygamous.

Let us now turn to the nectar- feeding insects ; we may suppose
the plant, of which we have been slowly increasing the nectar by
continued selection, to be a common plant ; and that certaiu
insects depended in main part on its nectar for food. I could give
many facts showing how anxious bees are to save time : for
instance, their habit of cutting holes and sucking the nectar at
the bases of certain flowers, which with a very little more trouble,
they can enter by the mouth. Bearing such facts in mind, it may
be believed that under certain circumstances individual differences
in the curvature or length of the proboscis, &c., too slight to be
appreciated, by us, might profit a bee or other insect, so that
certain individuals would be able to obtain their food more qmckly

Chap. iV.] NATURAL SELECTION. 75

than others ; and thus the communities to which they belonged
would flourish and throw off many swarms inheriting the same
peculiarities. The tubes of the corolla of the common red and
incarnate cloveis (Trifolium pratcnse and incarnatum) do not on a
hasty glance appear to differ in length ; yet the hive-bee can easily
Buck the nectar out of the incarnate clover, but not out of the
common red clover, which is visited by humble-bees alone ; so that
whole fields of the red clover offer in vain an abundant supply of
precious nectar to the hive- bee. That this nectar is much liked by
the hive-bee is certain ; for I have repeatedly seen, but only in the
autumn, many hive-bees sucking the flowers through holes bitten
in the base of the tube by humble-bees. The difference in the
length of the corolla in the two kinds of clover, which determines
the visits of the hive-bee, must be very trifling ; for I have been
assured that when red clover has been mown, the flowers of the
second crop are somewhat smaller, and that these are visited by
many hive-bees. I do not know whether this statement is accu-
rate; nor whether another published statement can be trusted,
namely, that the Ligurian bee, which is generally considered a
mere variety of the common hive-bee, and which freely crosses with
it, is able to reach and suck the nectar of the red clover. Thus, in
a country where this kind of clover abounded, it might be a great
advantage to the hive-bee to have a slightly longer or differently
constructed proboscis. On the other hand, as the fertility of this
clover absolutely depends on bees visiting the flowers, if humble-
bees were to become rare in any country, it might be a great
advantage to the plant to have a shorter or more deeply divided
corolla, so that the hive-bees should be enabled to suck its flowers.
Thus I can understand how a flower and a bee might slowly
become, either simultaneously or one after the other, modified and
adapted to each other in the most perfect manner, by the con-
tinued preservation of all the individuals which presented slight
deviations of structure mutually favourable to each other.

I am well aware that this doctrine of natural selection, exempli-
fied in the above imaginary instances, is open to the same objections
which were first urged against Sir Charles Lyell's noble views on
" the modern changes of the earth, as illustrative of geology ; " but
we now seldom hear the agencies which we see still at work, spoken
of as trifling or insignificant, when used in explaining the excavation
of the deepest valleys or the formation of long lines of inland
cliffs. Natural selection acts only by the preservation and accumu-
lation of small inherited modifications, each profitable to the pre-
served beinqi and as modern geology has almost banished such

76 ON THE INTERCROSSING OF INDIVIDUALS. [Chap. IT.

views as the excavation of a great valley by a single diluvial wave,
so will natural selection banish the belief of the continued creation
of new organic beings, or of any great and sudden modification in
their structure.

On the Intercrossing of Individuals.

I must here introduce a short digression. In the case of animals
and plants with separated sexes, it is of com'se obvious that two
individuals must always (with the exception of the curious and
not well-understood cases of parthenogenesis) unite for each birth ;
but in the case of hermaphrodites this is far from obvious.
Nevertheless there is reason to believe that with all hermaphrodites
two individuals, either occasionally or habitually, concur for the
reproduction of their kind. This view was long ago doubtfully
suggested by Sprengel, Knight and Kolreuter. We shall presently
see its importance ; but I must here treat the subject with extreme
brevity, though I have the materials prepared for an ample dis-
cussion. All vertebrate animals, all insects, and some other large
groups of animals, pair for each birth. Modern research has much
diminished the number of supposed hermaphrodites, and of real
hermaphrodites a large number pair ; that is, two individuals
regularly unite for reproduction, which is all that concerns us.
But still there are many hermaphrodite animals which certainly do
not habitually pair, and a vast majority of plants are hermaphro-
dites. What reason, it may be asked, is there for supposing in
these cases that tv/o individuals ever concur in reproduction ? As
it is impossible here to enter on details, I must trust to some
general considerations alone.

In the first place, I have collected so large a body of facts, and
made so many experiments, showing, in accordance with the almost
universal belief of breeders, that with animals and plants a cross
between different varieties, or between individuals of the same
variety but of another strain, gives vigour and fertility to the off-
spring ; and on the other hand, that close interbreeding diminishes
vigour and fertility ; that these facts alone incline me to believe
that it is a general law of nature that no organic being fertilises
itself for a perpetuity of generations; but that a cross with another
individual is occasionally — perhaps at long intervals of time —
indispensable.

On the belief that this is a law of nature, we can, I think, under-
etand several large classes of facts, such as the following, which
on any other view are inexplicable. Every hybridizer knows how
unfavourable exposure to wet is to the fertilisation of a flower, yel

Chap. IV.] ON THE INTERCROSSING OF INDIVIDUALS. 77

what a multitude of flowers have their anthers and stigmas fully
exposed to the weather ! If an occasional cross be indispensable,
notwithstanding that the plant's own anthers and pistil stand so
near each other as almost to ensure self-fertilisation, the fullest
freedom for the entrance of pollen from another individual will
explain the above state of exposure of the organs. Many flowers,
on the other hand, have their organs of fructification closely
enclosed, as in the great papilionaceous or pea-family ; but these
almost invariably present beautiful and curious adaptations in
relation to the visits of insects. So necessary are the visits of bees
to many papilionaceous flowers, that their fertility is greatly dimi-
nished if these visits be prevented. Now, it is scarcely possible for
insects to fly from flower to flower, and not to carry pollen from
one to the other, to the great good of the plant. Insects act like a
camel-hair pencil, and it is suflicient, to ensure fertilisation, just to
touch with the same brush the anthers of one flower and then the
stigma of another ; but it must not be supposed that bees would
thus produce a multitude of hybrids between distinct species ; for il
a plant's own pollen and that from another species are placed on
the same stigma, the former is so prepotent that it invariably and
completely destroys, as has been shown by Gartner, the influence
of the foreign pollen.

When the stamens of a flower suddenly spring towards the pistil,
or slowly move one after the other towards it, the contrivance
seems adapted solely to ensure self-fertilisation ; and no doubt it i-s
useful for this end : but the agency of insects is often required to
cause the stamens to spring forward, as Kolreuter has shown to be
the case with the barberry ; and in this very genus, which seems to
have a special contrivance for self-fertilisation, it is well known
that, if closely-allied forms or varieties are planted near each other,
it is hardly possible to raise pure seedlings, so largely do they
naturally cross. In numerous other cases, far from self-fertilisation
being favoured, there are special contrivances which effectually
prevent the stigma receiving pollen from its own flower, as I could
show from the works of Sprengel and others, as well as from my
own observations : for instance, in Lobelia fulgens, there is a really
beautiful and elaborate contrivance by which all the infinitely
numerous pollen-granules are swept out of the conjoined anthers of
each flower, before the stigma of that individual flower is ready to
receive them ; and as this flower is never visited, at least in my
garden, by insects, it never sets a seed, though by placing pollen
from one flower on the stigma of another, I raised plenty of seed-
lings. Another species of Lobelia, w^hich is visited by bees, seeds

78 ON THE INTERCROSSING OF INDIVIDUALS. [Chap. IV.

freely in my garden. In very many other cases, though there is no
special meciianical contrivance to prevent the stigma receiving
pollen from the same flower, yet, as Sprcngel, and more recently
Hildebrand, and others, have shown, and as I can confirm, either
the anthers burst befce the stigma is ready for fertihsation, or the
stigma is ready before the pollen of that flower is ready, so that
these so-named dichogamous plants have in fact separated sexes,
and must habitually be crossed. So it is with the reciprocally
dimorphic and trimorphic plants previously alluded to. How
strange are these facts ! How strange that the pollen and stigmatic
surface of the same flower, though placed so close together, as if for
the very purpose of self-fertilisation, should be in so many cases
mutually useless to each other ? How simply are these facts ex-
plained on the view of an occasional cross with a distinct individual
being advantageous or indispensable !

If several varieties of the cabbage, radish, onion, and of some
other plants, be allowed to seed near each other, a large majority of
the seedlings thus raised turn out, as I have found, mongrels : for
instance, I raised 233 seedling cabbages from some plants of different
varieties growing near each other, and of these only 78 were true to
their kind, and some even of these were not perfectly true. Yet
the pistil of each cabbage-flower is surrounded not only by its own
six stamens, but by those of the many other flowers on the same
plant ; and the pollen of each flower readily gets on its own stigma
without insect-agency ; for I have found that plants carefully
protected from insects produce the full number of pods. How,
then, comes it that such a vast number of the seedlings are mon-
grelized ? It must arise from the pollen of a distinct variety having
a prepotent effect over the flower's own pollen ; and that this is
part of the general law of good being derived from the intercrossing
of distinct individuals of the same species. When distinct species
are crossed the case is reversed, for a plant's own pollen is almost
always prepotent over foreign pollen ; but to this subject we shall
return in a future chapter.

In the case of a large tree covered with innumerable flowers, it
may be objected that pollen could seldom be carried from tree to
tree, and at most only from flower to flower on the same tree ; and
flowers on the same tree can be considered as distinct individuals
only in a limited sense. I believe this objection to be valid, but
that nature has largely provided against it by giving to trees a
strong tendency to bear flowers with separated sexes. When the
sexes are separated, althougJl the male and female flowers may be
produced on the same tree, pollen must be regularly carried from

Chap. I\'.] ON THE INTERCROSSING OF INDIVIDUALS. 79

flower to flower ; and this will give a better chance of pollen being
occasionally carried from tree to tree. That trees belonging to all
Orders have their sexes more often separated than other plants, I
find to be the case in this country ; and at my request Dr. Hooker
tabulated the trees of New Zealand, and Dr. Asa Gray those of the
United States, and the result was as I anticipated. On the other
hand, Dr. Hooker informs me that the rule does not hold good in
Australia ; but if most of the Australian trees are dichcgamous, the
same result would follow as if they bore flowers with separated
sexes. I have made these few remarks on trees simply to call
attention to the subject.

Turning for a brief space to animals : various terrestrial species
are hermaphrodites, such as the land-moUusca and earth-worms ;
but these all pair. As yet I have not found a single terrestrial
animal which can fertilise itself. This remarkable fact, which offers
so strong a contrast with terrestrial plants, is intelligible on the view
of an occasional cross being indispensable ; for owing to the nature of
the fertilising element there are no means, analogous to the action
of insects and of the wind with plants, by which an occasional cross
could be effected with terrestrial animals without the concurrence of
two individuals. Of aquatic animals, there are many self-fertilising
hermaphrodites ; but here the currents of water offer an obvious
means for an occasional cross. As in the case of flowers, I have as
yet failed, after consultation with one of the highest authorities,
namely. Professor Huxley, to discover a single hermaphrodite animal
with the organs of reproduction so perfectly enclosed that access
from without, and the occasional influence of a distinct individual,
can be shown to be physically impossible. Cirripedes long appeared
to me to present, under this point of view, a case of great difiSculty ;
but I have been enabled, by a fortunate chance, to prove that two
individuals, though both are self-fertilising hermaphrodites, do
sometimes cross.

It must have struck most naturalists as a strange anomaly that,
Ixjth with animals and plants, some species of the same family and
even of the same genus, though agreeing closely with each other in
their whole organisation, are hermaphrodites, and some unisexual.
Bnt if, in fact, all hermaphrodites do occasionally intercross, the
difi'erence between them and unisexual species is, as far as function
is concerned, very small.

From these several considerations and from the many special
facts which I have collected, but which I am unable here to give,
it appears that with animals and plants an occasional intercross
between distinct individuals is a very general, if not universal, law
of nat,iLre.

80 CIRCUMSTANCES FAVOURABLE TO THE [Chaf. IV.

Circumstances favourable for the production of new forms
through Natural Selection.

This is an extremely intricate subject. A great amount of varia-
bility, under which term individual differences are always includedj
will evidently be favourable. A large number of individuals, by
giving a better chance within any given period for the appearance
of profitable variations, will compensate for a lesser amount of
variability in each individual, and is, I believe, a highly important
element of success. Though Nature grants long periods of time for
the work of natural selection, she does not grant an indefinite
period ; for as all organic beings are striving to seize on each place
in the economy of nature, if any one species does not become modi-
fied and improved in a corresponding degree with its competitors, it
will be exterminated. Unless favourable variations be inherited by
some at least of the offspring, nothing can be effected by natural
selection. The tendency to reversion may often check or prevent the
work ; but as this tendency has not prevented man from forming
by selection numerous domestic races, why should it prevail against
natural selection ?

In the case of methodical selection, a breeder selects for some
definite object, and if the individuals be allowed freely to intercross,
his work will completely fail. But when many me\i, without
intending to alter the breed, have a nearly common standard of
perfection, and all try to procure and breed from the best animals,
improvement surely but slowly follows from this unconscious
process of selection, notwithstanding that there is no separation of
selected individuals. Thus it will be under nature ; for within a
confined area, with some place in the natural polity not perfectly
occupied, all the individuals varying in the right direction, though
in different degrees, will tend to be preserved. But if the area be
large, its several districts will almost certainly present different
conditions of life ; and then, if the same species undergoes modifi-
cation in different districts, the newly-formed varieties will intercross
on tbiB confines of each. But we shall see in the sixth chapter that
intermediate varieties, inhabiting intermediate districts, will in the
long run generally be supplanted by one of the adjoining varieties.
A. Intercrossing will chiefly affect those animals which unite for each

' birth and wander much, and which do not breed at a very quick

rate. Hence with animals of this nature, for instance, birds,
varieties will generally be confined to separated countries ; and this
I find to be the case. With hermaphrodite organisms which cross
only occasionally, and likewise with animals which unite for each

^^■

.oi

Chap. IV.] RESULTS OF NATURAL SELECTION. 81

birtb, but which wander little and can increase at a rapid rate, a
new and improved variety might be quickly formed on any one
spot, and might there maintain itself in a body and afterwards
spread, so that the individuals of the new variety would chiefly
cross together. On this principle, nurserymen always prefer saving
seed from a large body of plants, as the chance of intercrossing is
thus lessened.

Even with animals which unite for each birth, and which do not
propagate rapidly, we must not assume that free intercrossing would
always eliminate the effects of natural selection ; for I can bring
forward a considerable body of facts showing that within tlie same
area, two varieties of the same animal may long remain distinct,
from haunting different stations, from breeding at slightly different
seasons, or from the individuals of each variety preferring to pair
together.

Intercrossing plays a very important part in nature by keeping
the individuals of the same species, or of the same variety, true and
imiform in character. It will obviously thus act far more efficiently
with those animals which unite for each birth ; but, as already stated,
we have reason to believe that occasional intercrosses take place with
all animals and plants. Even if these take place only at long inter-
vals of time, the young thus produced will gain so much in vigour
and fertility over the offspring from long-continued self- fertilisation,
that they will have a better chance of surviving and propagating
their kind ; and thus, in the long run, the influence of crosses, even
at rare intervals, will be great. With respect to organic beings
extremely low in the scale, which do not propagate sexually, nor
conjugate, and which cannot possibly intercross, uniformity of cha-
racter can be retained by them under the same conditions of life,
only through the principle of inheritance, and through natural selec-
tion which will destroy any individuals departing from the proper
type. If ihe conditions of life change and the form undergoes modifi-
cation, uniformity of character can be given to the modified offspring,
solely by natural selection preserving similar favourable variations.

Isolation, also, is an important element in the modification of
species through natural selection. In a confined or isolated area, if
not very large, the organic and inorganic conditions of life will
generally be almost uniform ; so that natural selection will tend to
modify all the varying individuals of the same species in the same
manner. Intercrossing with the inhabitants of the surrounding dis-
tricts will, also, be thus prevented. Moritz Wagner has lately pub-
lished an interesting essay on this subject, and has shown that the
service rendered by isolation in preventing crosses between newly-

G

82 CIRCUMSTANCES FAVOURABLE TO THE [Chap. IV

foiined varieties is probably greater even than I supposed. But
from reasons already assigned I can by no means agree with this
naturalist, that migration and isolation are necessary elements for
the formation of new species. The importance of isolation is like-
wise great in preventing, after any physical change in the conditions,
such as of climate, elevation of the land, &c., the immigration of
better adapted organisms; and thus new places in the natural
economy of the district will be left open to be filled up by the
modification of the old inhabitants. Lastly, isolation will give time
for a new variety to be improved at a slow rate ; and this may some-
times be of much importance. If, however, an isolated area be very
small, either from being surrounded by barriers, or from having very
peculiar physical conditions, the total number of the inhabitants
will be small ; and this will retard the production of new species
through natural selection, by decreasing the chances of favourable
variations arising.

The mere lapse of time by itself does nothing, either for or against
natural selection. I state this because it has been erroneously
asserted that the element of time has been assumed by me to play
an all-important part in modifying species, as if all the forms of life
were necessarily undergoing change through some innate law. Lapse
of time is only so far important, and its importance in this respect
is great, that it gives a better chance of beneficial variations arising,
and of their being selected, accumulated, and fixed. It likewise
lends to increase the direct action of the physical conditions of life,
in relation to the constitution of each organism.

If we turn to nature to test the truth of these remarks, and look
at any small isolated area, such as an oceanic island, although the
number of species inhabiting it is small, as we shall see in our
chapter on Geographical Distribution ; yet of these species a very
large proportion are endemic, — that is, have been produced there,
and nowhere else in the world. Hence an oceanic island at first
sight seems to have been highly favourable for the production of
new species. But we may thus deceive ourselves, for to ascertain
whether a small isolated area, or a large open area like a continent,
has been most favourable for the production of new organic forms,
we ought to make the comparison within equal times ; and this we
are incapable of doing.

Although isolation is of great importance in the production of new
species, on the whole I am inclined to believe that largeness of area
is still more important, especially for the production of species which
shall prove capable of enduring for a long period, and cf spreading
widely. Throughout a great and open area, not only will there be a

Chap, n.] RESULTS OF NATUKAL SELECTION. 83

better chance of favourable variations, arising from the large number
of individuals of the same species there supported, but the conditions
of life are much more complex from the large number of already-
existing species ; and if some of these many species become modified
and improved, others will have to be improved in a corresponding
degree, or they will be exterminated. Each new form, also, as soon
as it has been much improved, will be able to spread over the open
and continuous area, and will thus come into competition with
many other forms. Moreover, great areas, though now continuous,
will often, owing to former oscillations of level, have existed in r,
broken condition ; so that the good effects of isolation will generally,
to a certain extent, have concurred. Finally, I conclude that,
although small isolated areas have been in some respects highly
favourable for the production of new species, yet that the course of
modification will generally have been more rapid on large areas ;
and what is more important, that the new forms produced on large
areas, which already have been victorious over many competitors,
will be those that will spread most widely, and will give rise to the
greatest number of new varieties and species. They will thus play
a more important part in the .changing history of the organic
world.

, In accordance with this view, we can, perhaps, understand some
facts which will be again alluded to in our chapter on Geographical
Distribution ; for instance, the fact of the productions of the smaller
continent of Australia now yielding before those of the larger
Europa30-Asiatic area. Thus, also, it is that continental productions
have everywhere become so largely naturalised on islands. On a
small island, the race for life will have been less severe, and there
will have been less modification and less extermination. Hence, we
can understand how it is that the flora of Madeira, according to
Oswald Heer, resembles to a certain extent the extinct tertiary flora
of Europe. All fresh-water basins, taken together, make a small
area compared with that of the sea or of the land. Consequently,
the competition between fresh- water productions will have been less
severe than elsewhere ; new forms will have been then more slowly
produced, and old forms more slowly exterminated. And it is in
fresh-water basins that we find seven genera of Ganoid fishes,
remnants of a once preponderant order : and in fresh water we find
some of the most anomalous forms now known in the world, as tho
Ornithorhynchus and Lepidosiren, which, like fossils, connect to a
certain extent orders at present widely sundered in the natural
scale. These anomaliDUS forms may be called living fossils; they
have endured to the present day, from having inhabited a confined

o 2

84 CIRCUMSTANCES FAVOURABLE TO THE [Chap. IT.

area, and from having been exposed to less varied, and therefore less
severe, competition.

To sum up, as far as the extreme intricacy of the subject permits,
the circumstances favourable and anfavourable for the production of
new species through natural selection. I conclude that for terrestrial
productions a large continental area, which has undergone many
oscillations of level, will have been the most favourable for the pro-
duction of many new forms of life, fitted to endure for a long time
and to spread widely. Whilst the area existed as a continent, the
inhabitants will have been numerous in individuals and kinds, and
will have been subjected to severe competition. "When converted
by subsidence into large separate islands, there will still have existed
many individuals of the same species on each island : intercrossing
on the confines of the range of each new species will have been
checked : after physical changes of any kind, immigration will have
been prevented, so that new places in the polity of each island will
have had to be filled up by the modification of the old inhabitants ;
and time will have been allowed for the varieties in each to become
well modified and perfected. When, by renewed elevation, the
islands were reconverted into a continental area, there will again
have been very severe compciition : the most favoured or improved
varieties will have been enabled to spread : there will have been
much extinction of the less improved forms, and the relative propor-
tional numbers of the various inhabitants of the reunited continent
will again have been changed ; and again there will have been a fair
field for natural selection to improve still further the inhabitants,
and thus to produce new species.

That natural selection generally acts with extreme slowness I fully
admit. It can act only when there are places in the natural polity
of a district which can be better occupied by the modification of
some of its existing inhabitants. The occurrence of such places will
often depend on physical changes, which generally take place very
slowly, and on the immigration of better adapted forms being pre-
vented. As some few of the old inhabitants become modified,
tne mutual relations of others will often be disturbed ; and this
will create new places, ready to be filled up by better adapted forms;
but all this will take place very slowly. Although all the indi-
viduals of the same species differ in some slight degree from each
other, it would often be long before differences of the right nature
in various parts of the organisation might occur. The result would
often be greatly retarded by free intercrossing. Many will exclaim
that these several causes are amply sufficient to neutralise the power
of natural selection. I do not believe so. But I do believe that

Omap. IV.j RESULTS OF NATURAL SELECTION. 85

natural selection will generally act very slowly, only at long intervals
of time, and only on a few of the inhabitants of the same region. I
further believe that these slow, intermittent results accord well
with what geology tells us of the rate and manner at which the in-
habitants of the world have changed.

Slow though the process of selection may be, if feeble man can
do much by artificial selection, I can see no limit to the amount of
change, to the beauty and complexity of the coadaptations between
all organic beings, one with another and with their physical con-
ditions of life, which may have been effected in the long course of
time through nature's power of selection, that is by the survival
of the fittest.

Extinction caused hy Natural Selection.

This subject will be more fully discussed in our chapter on
Geology ; but it must here be alluded to from being intimately con-
nected with natural selection. Natural selection acts solely through
the preservation of variations in some way advantageous, which
consequently endure. Owing to the high geometrical rate of increase
of all organic beings, each area is already fully stocked with inhabit-
ants ; and it follows from this, that as the favoured forms increase in
number, so, generally, will the less favoured decrease and become
rare. Earity, as geology tells us, is the precursor to extinction. We
can see that any form which is represented by few individuals will
run a good chance of utter extinction, during great fluctuations in
the nature of the seasons, or from a temporary increase in the number
of its enemies. But we may go further than this ; for, as new forms
are produced, unless we admit that specific forms can go on indefi-
nitely increasing in number, many old forms must become extinct.
That the number of specific forms has not indefinitely increased,
geology plainly tells us ; and we shall presently attempt to show
why it is that the number of species throughout the world has not
"become immeasurably great.

We have seen that the species which are most numerous in indi-
viduals have the best chance of producing favourable variations
within any given period. We have evidence of this, in the facts
stated in the second chapter, showing that it is the common and
diffused or dominant species which offer the greatest number of
recorded varieties. Hence, rare species will be less quickly modified
or improved within any given i)eriod ; they will consequently bo
beaten in the race for life by the modified and improved descendants
of the commoner species.

From these several considerations I think it inevitably follows,

86 EXTINCTION BY NATURAL SELECTION. [Chap. IV.

that as new species in the course of time are formed through natural
selection, others will become rarer and rarer, and finally extinct.
The forms which stand in closest competition with those undergoing
modification and Improvement, will naturally suffer most. And we
have seen in the chapter on the Struggle for Existence that it is the
most closely-allied forms, — varieties of the same species, and species
of the same genus or of related genera, — which, from having nearly
the same structure, constitution, and habits, generally come into
the severest competition with each other ; consequently, each new
variety or species, during the progress of its formation, will generally
press hardest on its nearest kindred, and tend to exterminate them.
We see the same process of extermination amongst our domesticated
productions, through the selection of improved forms by man.
Many curious instances could be given showing how quickly new
breeds of cattle, sheep, and other animals, and varietieij of flowers,
take the place of older and inferior kinds. In Yorkshire, it is
historically known that the ancient black cattle were displaced by
the long-horns, and that these "were swept away by the short-
horns *' (I quote the words of an agricultural writer) " as if by s'>^ae
murderous pestilence."

Divergence of Character.

The principle, which I have designated by this term, is of high
importance, and explains, as I believe, several important facts. In
the first place, varieties, even strongly-marked ones, though having
somewhat of the character of species — as is shown by the hopeless
doubts in many cases how to rank them — yet certainly differ far
less from each other than do good and distinct species. Keverthe-
less, according to my view, varieties are species in the process of
formation, or are, as I have called them, incipient species. How,
then, does the lesser difference between varieties become augmented
into the greater difference between species ? That this does habitu-
ally happen, we must infer from most of the innumerable species
throughout nature presenting well-marked differences ; whereas
varieties, the supposed prototypes and parents of future well-marked
species, present slight and ill-defined differences. Mere chance, as
we may call it, might cause one variety to differ in some character
from its parents, and the offspring of this variety again to differ
from its parent in the very same character and in a greater degree ;
but this alone would never account for so habitual and large
a degree of difference as that between the species of the same
genus.

As has always been my practice, I have sought light on this

CHAP. IV.] DIVERGENCE OF CHARACTER. 87

head from our domestic productions. We shall here find something
analogous. It will be admitted that the production of races so
different as short-horn and Hereford cattle, race and cart horses,
the several breeds of pigeons, &c., could never have been effected by
the mere chance accumulation of similar variations during many
successive generations. In practice, a fancier is, for instance, struck
by a pigeon having a slightly shorter beak; another fancier is
struck by a pigeon having a rather longer beak; and on the
acknowledged principle that " fanciers do not and will not admire
a medium standard, but like extremes," they both go on (as has
actually occurred with the sub-breeds of the tumbler-pigeon)
choosing and breeding from birds with longer and longer beaks, or
with shorter and shorter beaks. Again, we may suppose that at an
early period of history, the men of one nation or district required
swifter horses, whilst those of another required stronger and bulkier
horses. The early differences would be very slight ; but, in the
course of time, from the continued selection of swifter horses in
the one case, and of stronger ones in the other, the differences would
become greater, and would be noted as forming two sub-breeds.
Ultimately, after the lapse of centuries, these sub-breeds would
become converted into two well-established and distinct breeds. As
the differences became greater, the inferior animals v;ith interme-
diate characters, being neither very swift nor very strong, would
not have been used for breeding, and will thus have tended to dis-
appear. Here, then, we see in man's productions the action of what
may be called the principle of divergence, causing differences, at
first barely appreciable, steadily to increase, and the breeds to
diverge in character, both from each other and from their common
parent.

But how, it may be asked, can any analogous principle apply in
nature ? I believe it can and does apply most efficiently (though it
was a long time before I saw how), from the simple circumstance
that the more diversified the descendants from any one species
become in structure, constitution, and habits, by so much will they
bo better enabled to seize on many and widely diversified places
in the polity of nature, and so be enabled to increase in numbers.

We can clearly discern this in the case of animals with simple
habits. Take the case of a carnivorous quadruped, of which the
number that can be supported in any country has long ago arrived
at its full average. If its natural power of increase be allowed to
act, it can succeed in increasing (the country not undergoing any
change in conditions) only by its varying descendants seizing on
places at present occupied by ether animals: some of them, foi

88 DIVERGENCE OF CHARACTEK. [Chap. IV.

instance, being enabled to feed on new kinds of prey, either dead
or alive ; some inhabiting now stations, climbing trees, frequenting
water, and some perhaps becoming less carnivorous. The more
diversified in habits and structure the descendants of our carnivo-
rous animals become, the more places they will be enabled to occupy.
What applies to one animal will apply throughout all time to all
animals — that is, if they vary— for otherwise natural selection car..
eiiect nothing. So it will be with plants. It has been experi-
mentally proved, that if a plot of ground be sown with one species
oi grass, and a similar plot be sown with several distinct genera of
grasses, a greater number of plants and a greater weight of dry
herbage can be raised in the latter than in the former case. The
same has been found to hold good when one variety and several
mixed varieties of wheat have been sown on equal spaces of ground.
Hence, if any one species of grass were to go on varyimi;, and the
varieties were continually selected which differed from each other
in the same manner, though in a very slight degree, as do the
distinct species and genera of grasses, a greater number of individual
plants of this species, including its modified descendants, would
succeed in living on the same piece of ground. And we know that
each species and each variety of grass is annually sowing almost
countless seeds ; and is thus striving, as it may be said, to the
utmost to increase in number. Consequently, in the course of many
thousand generations, the most distinct varieties of any one species
of grass would have the best chance of succeeding and of increasing
in numbers, and thus of supplanting the less distinct varieties ; and
varieties, when rendered very distinct from each other, take the rank
of species.

The truth of the principle that the greatest amount of life can be
supported by great diversification of structure, is seen under many
natural circumstances. In an extremely small area, especially if
freely open to immigration, and where the contest between indivi-
dual and individual must be very severe, we always find great
diversity in its inhabitants. For instance, I found that a piece of
turf, three feet by four in size, which had been exposed for many
years to exactly the same conditions, supported twenty species of
plants, and these belonged to eighteen genera and to eight orders,
which shows how much these plants differed from each other. So
it is with the planis and insects on small and uniform islets : also
in small ponds of fresh water. Farmers find that they can raise
most food by a rotation of plants belonging to the most different
orders : nature; follows what may be called a simultaneous rotation.
Most of the animals and plants which live close round any small

Chap. IV.] DIVERGENCE OF CHARACTER. 89

piece of ground, could live on it (supposing its nature not to be in
any way peculiar), and may be said to be striving to the utmost to
live there ; but, it is seen, that where they come into the closest
competition, the advantages of diversification of structure, with the
accompanying dififerences of habit and constitution, determine
that the inhabitants, which thus jostle each other most closely,
shall, as a general rule, belong to what we call different genera
and orders.

The same principle is seen in the naturalisation of plants through
man's agency in foreign lands. It might have been expected that
the plants which would succeed in becoming naturalised in any
land would generally have been closely allied to the indigenes ; for
these are commonly looked at as specially created and adapted
for their own country. IL might also, perhaps, have been expected
rhat naturalised plants would have belonged to a few groups more
especially adapted to certain stations in their new homes. But the
case is very different ; and Alph. de Candolle has well remarked, in
his great and admirable work, that floras gain by naturalisation,
proportionally with the number of the native genera and species,
far more in new genera than in new species. To give a single
instance: in the last edition of Dr. Asa Gray's * Manual of the
Flora of the Northern United States,' 2G0 naturalised plants are
enumerated, and these belong to 162 genera. We thus see that
these naturalised plants are of a highly diversified nature. They
differ, moreover, to a large extent, from the indigenes, for out of the
102 naturalised genera, no less than 100 genera are not there indi-
genous, and thus a large proportional addition is made to the genera
now living in the United States.

By considering the nature of the plants or animals which have in
any country struggled successfully with the indigenes, and have
there become naturalised, we may gain some crude idea in what
manner some of the natives would have to be modified, in order to
gain an advantage over their compatriots; and we may at least
infer that diversification of structure, amounting to new generic
differences, would be profitable to them.

The advantage of diversification of structure in the inhabitants
of the same region is, in fact, the same as that of the physiological
division of labour in the organs of the same individual body — a
subject so well elucidated by Milne Edwards. No physiologist
doubts that a stomach adapted to digest vegetable matter alone, or
flesh alone, draws most nutriment from these substances. So in the
general economy of any land, the more widely and perfectly the
animals and plants are diversified for different habits of life, so will

90 RESULTS OF THE ACTION OF [Chap. IV

a greater number of individuals be capable of there supporting
themselves. A set of animals, with their organisation but little
diversified, could hardly compete with a set more perfectly diversified
in structure. It may be doubted, for instance, whether the Austra-
lian marsupials, which are divided into groups diff'eriDg but little
from each other, and feebly representing, as Mr. Waterhouse and
others have remarked, our carnivorous, ruminant, and rodent mam-
mals, could successfully compete with these well-developed orders.
In the Australian mammals, we see the process of diversification in
an early and incomplete stage of development.

The ProhaUe Effects of the Action of Natural Selection through
Divergence of Character and Extinction^ on the Descendants of
a Common Ancestor.

After the foregoing discussion, which has been much compressed,
wo may assume that the modified descendants of any one species
will succeed so much* the better as they become more diversified in
structure, and are thus enabled to encroach on places occupied by
other beings. Now let us see how this principle of benefit being
derived from divergence of character, combined with the principles
of natural selection and of extinction, tends to act.

The accompanying diagram will aid us in understanding this
rather perplexing subject. Let A to L represent the species of a
genus large in its own country ; these species are supposed to
resemble each other in unequal degrees, as is so generally the case
in nature, and as is represented in the diagram by the letters
standing at unequal distances. I have said a large genus, because
as we sav/ in the second chapter, on an average more species vary in
large genera than in small genera ; and the varying species of the
large genera present a greater number of varieties. We have, also,
seen that the species, which are the commonest and the most widely
diffused, vary more than do the rare and restricted species. Let (A)
be a common, widely-diffused, and varying species, belonging to a
genus large in its own country. The branching and diverging
dotted lines of unequal lengths proceeding from (A), may represent
its varying offspring. The variations arc supposed to be extremely
slight, but of the most diversified nature ; they are not supposed all
to appear simultaneously, but often after long intervals of time ; nor
are they all supposed to endure for equal periods. Only those
variations which are in some way profitable will be preserved or
naturally selected. And here the importance of the principle of
benefit derived from divergence of character comes in ; for this will
generally lead to the most different cr divergent variations (repre-

Chap. IV.] NATURAL SELECTION. 51

sented by the outer dotted lines) being preserved and accumulated
by natural selection. When a dotted line reaches one of the hori-
zontal lines, and is there marked by a small numbered letter, a
sufficient amount of variation is sup[iused to have been accumulated
to form it into a fairly well-mark ed^ variety, such as would be
thought worthy of record in a systematic work.

The intervals between the horizontal lines in the diagram, may
represent each a thousand or more generations. After a thousand
generations, species (A) is supposecTTo' Have produced two fairly
well-marked varieties, namely a} and rn}. These two varieties will
generally still be exposed to the same conditions which made their
parents variable, and the tendency to variability, is injtself Jieredi-
tary ; consequently they will likewise tend to vary, and commonly
in nearly the same manner as did their parents. ^Moreover, these
two varieties, being only slightly modified forms, will tend to inherit
those advantages which made their parent (A) more numerous than
most of the other inhabitants of the same country ; they will also
partake of those more general advantages which made the genus to
which the jmrent-species belonged, a large genus in its own country.
And all these circumstances are favourable to the production of new
varieties.

If, then, these two varieties be variable, the most divergent of
their variations will generally be yireserved during the next thousand
generations. And after this interval, variety a^ is supposed in the
diagram to have produced variety a^, which will, owing to the prin-
ciple of divcrg.en,cc, differ more from CA) than did variety a}.
Yariefym* is supposed to have produced two varieties, namely m^
and s^, differing from each other, and more considerably from their
common parent (A). We may continue the process by similar
steps for any length of time ; some of the varieties, after each
thousand generations, producing only a single variety, but in a more
and more modified condition, some producing two or three varieties,
and some failing to produce any. Thus the varieties or modified
descendants of the common parent (A), will generally go on
increasing in number and diverging in character. In the diagram
the process is represented up to the ten-thousandth generation, and
under a condensed and simplified form up to the fourteen-thousandth
generation.

But I must here remark that I do not suppose that the process
ever goes on so regularly as is represented in the diagram, though in
itself made somewhat irregular, nor that it goes on continuously ; it
is far more probable that each form remjiins for long periods unal-
tered, and then again undergoes modification.^ Nor dc I suppose

32 RESULTS OF THE ACTION OF [Chap. IV

that the most divergent varietiss are invariably preserved: a
medium form may often long endure, and may or may not produce
more than one modified descendant; for natural selection will
always act according to the nature of the places which are either
unoccupied or not perfectly occupied by other beings ; and this will
depend on infinitely complex relations. But as a general rule, the
more diversified in structure the descendants from any one species
can be rendered, the more places they will be enabled to seize on,
and the more their modified progeny will increase. In our diagram
the line of succession is broken at regular intervals by small num-
bered letters marking the successive forms which have become
sufficiently distinct to be recorded as varieties. But these breaks
are imaginary, and might have been inserted anywhere, after inter-
vals long enough to allow the accumulation of a considerable amount
of divergent variation.

As all the modified descendants from a common and widely-
diffused species, belonging to a large genus, will tend to imrtake
of the same advantages which made their parent successful in
life, they will generally go on multiplying in number as well as
diverging in character : this is represented in the diagram by the
several divergent branches proceeding from (A). The modified
offspring from the later and more highly improved branches in the
lines of descent, will, it is probable, often take the place of, and so
destroy, the earlier and less improved branches : this is represented
in the diagram by some of the lower branches not reaching to the
upper horizontal lines. In some cases no doubt the process of
modification v/ili be confined to a single line of descent, and the
number of modified descendants will not be increased ; although
the amount of divergent modification rnay have been augmented.
This case would he represented in the diagram, if all the lines pro-
ceeding from (A) were removed, excepting that from a} to a^^. In
the same way the English race-horse and English pointer have appa-
rently both gone on slowly diverging in character from their original
stocks, without either having given off any fresh branches or races.

After ten thousand generations, species (A) is supposed to have
produced three forms, a^°,/^°, and m^°, which, from having diverged
in character during the successive generations, will have come to
differ largely, but perhaps unequally, from each other and from
their common parent. If we suppose the amount of change be-
tween each horizontal line in our diagram to be excessively small,
these three forms may still be only well-marked varieties ; but we
have only to suppose the steps in the process of modification to be
more numerous or greater in amount, to convert these three forms

Chap. IV.] NATURAL SELECTION. 93

Id to doubtful or at last into well-defined species. Thus the diagram
illustrates the steps by which the small differences distinguishing
varieties are increased into the larger differences distinguishing spe-
cies. By continuing the same process for a greater number of gene-
rations (as shown in the diagram in a condensed and simplified
manner), we get eight species, marked by the letters between a^*
and m^*j all descended from (A). Thus, as I believe, species are
multiplied and genera are formed.

In a large genus it is probable that more than one species would
vary. In the diagram I have assumed that a second species (I) has
produced, by analogous steps, after ten thousand generations, either
two well-marked varieties (w^^ and 2^°) or two species, according to
the amount of change supposed to be represented between the hori-
zontal lines. After fourteen thousand generations, six new species,
marked by the letters n^^ to z^'^, are supposed to have been produced.
In any genus, the species which are already very difi'erent in cha-
racter from each other, will generally tend to produce the greatest
number of modified descendants ; for these will have the best
chance of seizing on new and widely different places in the polity
of nature : hence in the diagram I have chosen the extreme species
(A), and the nearly extreme species (I), as those which have largely
varied, and have given rise to new varieties and species. The other
nine species (marked by capital letters) of our original genus, may
for long but unequal periods continue to transmit unaltered de-
scendants ; and this is shown in the diagram by the dotted lines
unequally prolonged upwards.

But during the process of modification, represented in the dia-
gram, another of our principles, namely that of extinction, will have
played an important part. As in each fully stocked country natural
selection necessarily acts by the selected form having some advan-
tage in the struggle for life over other forms, there will be a constant
tendency in the improved descendants of any one species to sup-
glantand exterminat^e in each stage of descent their predecessors
and their original progenitor. For it should be remembered that
the competition will generally be most severe between those forms
which are most nearly related to each other in habits, constitution,
and structure. Hence all the intermediate forms between the earlier
and later states, that is between the less and more improved states
of the same species, as well as the original parent-species itself, will
generally tend to become extinct. So it probably will be with many
whole collateral lines of descent, which will be conquered by later
and improved lines. If, however, the modified ofi'spring of a species
get into some distinct country, or become quickly adapted to some

State HisTf^ric;;-?! a^-.O

94 RESULTS OF THE ACTION OF [Chap. IV.

puite new station, in which offspring and progenitor do not come
-nto competition, both may continue to exist.

If, then, our diagram be assumed to represent a considerable
amount of modification, species (A) and all the earlier varieties will
have become extinct, being replaced by eight new species (a}^ to
m") ; and species (I) will be replaced by six {71^* to 2") new species.

But we may go further than this. The original species of our
genus were supposed to resemble each other in unequal degrees, as
is so generally the case in nature ; species (A) being more nearly
related to B, 0, and D, than to the other species ; and species (1)
more to G, H, K, L, than to the others. These two species (A) and
(T) were also supposed to be very common and widely diffused
species, so that they must originally have had some advantage over
most of the other species of the genus. Their modified descendants,
fourteen in number at the fourteen-thousandth generation, will
probably have inherited some of the same advantages : they have
also been modified and improved in a diversified manner at each
stage of descent, so as to have become adapted to many related
places in the natural economy of their country. It seems, therefore,
extremely probable that they will have taken the places of, and
thus exterminated, not only their parents (A) and (I), but likewise
some of the original species which were most nearly related to their
parents. Hence very few of the original species will have trans-
mitted offspring to the fourteen-thousandth generation. We may
suppose that only one (F), of the two species (E and F) which were
least closely related to the other nine original species, has trans-
mitted descendants to this late stage of descent.

The new species in our diagram descended from the original
eleven species, will now be fifteen in number. Owing to the diver-
gent tendency of natural selection, the extreme amount of difference
in character between species a^* and 2'* will be much greater than
that between the most distinct of the original eleven species. The
new species, moreover, will be allied to each other in a widely dif-
ferent manner. Of the eight descendants from (A) the three marked
a}\ 2^^, p^\ will be nearly related from having recently branched off
from a^^ ; h^'^, and /^*, from having diverged at an earlier period from
o^, will be in some degree distinct from the three first-named species ;
and lastly, 0^^, e^^, and m^*, will be nearly related one to the other,
but, from having diverged at the first commencement of the process
of modification, will be widely different from the other five species,
and may constitute a sub-genus or a distinct genus.

The six descendants from (I) will form two sub-genera or genera.
But as the original spicies (I) differed largely from (A), standing

Chap. IV.] NATURAL SELECTION. 95

nearly at the extreme end of the original genus, the six descendants
from (I) will, owing to inheritance alone, differ considerably from
the eight descendants from (A) ; the two groups, moreover, are
supposed to have gone on diverging in different directions. The
intermediate species, also (and this is a very important considera-
tion), which connected the original species (A) and (I), have all
become, excepting (F), extinct, and have left no descendants.
Hence the six new species descended from (I), and the eight de-
scended from (A), will have to be ranked as very distinct genera,
or even as distinct sub-families.

Thus it is, as I believe, that two or more genera are produced
by descent with modification, from two or more species of the same
genus. And the two or more parent-species are supposed to be
descended from some one species of an earlier genus. In our dia-
gram, this is indicated by the broken lines, beneath the capital
letters, converging in sub-branches downwards towards a single
point ; this point represents a species, the supposed progenitor of our
several new sub-genera and genern..

It is worth while to reflect for a moment on the character of the
new species r^^, which is supposed not to have diverged much in
character, but to have retained the form of (F), either unaltered or
altered only in a slight degree. In this case, its affinities to the
other fourteen new species will be of a curious and circuitous nature.
Being descended from a form which stood between the parent-species
(A) and (I), now supposed to be extinct and unknown, it will be
in some degree intermediate in character between the two groups
descended from these two species. But as these two groups have
gone on diverging in character from the type of their parents, the
new species (f^-*) will not be directly intermediate between them,
but rather between types of the two groups ; and every naturalist
will be able to call such cases before his mind.

In the diagram, each horizontal line has hitherto been supposed
to represent a thousand generations, but each may represent a
million or more generations ; it may also represent a section of the
successive strata of the earth's crust including extinct remains. We
shall, when we come to our chapter on Geology, have to refer again
to this subject, and I think we shall then see that the diagram
throws light on the affinities of extinct beings, which, though gene-
rally belonging to the same orders, families, or genera, with those
now living, yet are often, in some degree, intermediate in character
oetween existing groups ; and we can understand this fact, for the
extinct species lived at various remote epochs when the branching
lines of descent had diversred less.

96 RESULTS OF THE ACTION OF [Chap. IV

I see no reason to limit the process of modification, as now ex-
plained, to the formation of genera alone. If, in the diagram, we
suppose the amount of change represented by each successive group
of diverging dotted lines to be great, the forms marked a}^ to p^^,
those marked b^'^ and f^\ and those marked o" to m^^, will form
three very distinct genera. We shall also have two very distincfc
genera descended from (I), differing widely from the descendants
of (A). These two groups of genera will thus form two distinct
families, or orders, according to the amount of divergent modifica-
tion supposed to be represented in the diagram. And the two new
families, or crders, are descended from two species of the original
genus, and these are supposed to be descended from some still more
ancient and unknown form.

We have seen that in each country it is the species belonging
to the larger genera which oftenest present varieties or incipient
species. This, indeed, might have been expected ; for, as natural
selection acts through one form having some advantage over other
forms in the struggle for existence, it will chiefly act on those which
already have some advantage; and the largeness of any group
shows that its species have inherited from a common ancestor some
advantage in common. Hence, the struggle for the production of
new and modified descendants will mainly lie between the larger
groups which are all trying to increase in number. One large group
will slowly conquer another large group, reduce its numbers, and
thus lessen its chance of further variation and improvement.
Within the same large group, the later and more highly perfected
sub-groups, from branching out and seizing on many new places in
the polity of Nature, will constantly tend to supplant and destroy
the earlier and less improved sub-groups. Small and broken groups
and sub-groups will finally disappear. Looking to the future, we
can predict that the groups of organic beings which are now large
and triumphant, and which are least broken up, that is, which have
as yet suffered least extinction, will, for a long period, continue to
increase. But which groups will ultimately prevail, no man can
predict ; for we know that many groups, formerly most extensively
developed, have now become extinct. Looking still more remotely
to the future, we mny predict that, owing to the continued and
steady increase of the larger groups, a multitude of smaller groups
will become utterly extinct, and leave no modified descendants;
and consequently that, of the species living at any one period,
extremely few will transmit descendants to a remote futurity. 1
shall have to return to this subject in the chapter on Classification,
but I may add that as, according to this view, extremely few of the

Chap. IV.] NATURAL SELECTION. »7

more ajicient species have transmitted descendants to the present
day, and, as all the descendants of the same species form a class, we
can miderstand how it is that there exists so few classes in each
main division of the animal and vegetable kingdoms. Although
few of the most ancient species have left modified descendants, yet,
at remote geological periods, the earth may have been almost as
well peopled with species of many genera, families, orders, and
classes, as at the present time.

On the Degree to which Organisation tends to advance.

Natural Selection acts exclusively by the preservation and accu-
mulation of variations, which are beneficial under the organic and
inorganic conditions to which each creature is exposed at all periods
of life. The ultimate result is that each creature tends to become
more and more improved in relation to its conditions. This im-
provement inevitably leads to the gradual advancement of the
organisation of the greater number of living beings throughout the
world. But here we enter on a very intricate subject, for naturalists
have not defined to each other's satisfaction what is meant by an
advance in organisation. Amongst the vertebrata the degree of
intellect and an approach in structure to man clearly come into
play. It might be thought that the amount of change which the
various parts and organs pass through in their development from
the embryo to maturity would suffice as a standard of comparison ;
but there are cases, as with certain parasitic crustaceans, in which
several parts of the structure become less perfect, so that the mature
animal cannot be called higher than its larva. Von Baer's standard
seems the most widely applicable and the best, namely, the amount
of differentiation of the parts of the same organic being, in the
adult state as I should be inclined to add, and their specialisa-
tion for different functions ; or, as Milne Edwards would express it,
the compkteness__of Jihe dLvision of physiological labour. . But we
shall see how obscure this subject is if we look, for instance, to fishes,
amongst which some naturalists rank those as highest which, like
the sharks, approach nearest to amphibians ; whilst other naturalists
rank the common bony or teleostean fishes as the highest, inasmuch
as they are most strictly fish-like, and differ most from the other
vertebrate classes. We see still more plainly the obscurity of the
subject by turning to plants, amongst which the standard of intel-
lect is of course quite excluded ; and here some botanists rank those
plants as highest which have every organ, as sepals, petals, stamens,
and pistils, fully developed in each flower ; whereas other botanists,

H

98 ON THE DEGREE TO WHICH [Chap, IV.

probably with more truth, look at the plants which have theii
HBveral organs much modified and reduced in number as the
highest.

If we take as the standard of high organisation the amount ol
differentiation and specialisation of the several organs in each being
when adult (and this will include the advancement of the brain for
intellectual purposes), natural selection clearly leads towards this
standard : for all physiologists admit that the specialisation of organs,
inasmuch as in this state they perform their functions better, is an
advantage to each being ; and hence the accumulation of variations
tending towards specialisation is within the scope of natural selec-
tion. On the other hand, we can see, bearing in mind that all
organic beings are striving to increase at a high ratio and to seize on
every unoccupied or less well occupied place in the economy of
nature, that it is quite possible for natural selection gradually to fit
a being to a situation in which several organs would be superfluous
or useless : in such cases there would be retrogression in the scale of
organisation. Whether organisation on the whole has actually
advanced from the remotest geological periods to the present day
will be more conveniently discussed in our chapter on Geological
Sjicceaaion.

But it may be objected that if all organic beings thus tend to
rise in the scale, how is it that throughout the world a multitude of
the lowest forms still exist ; and how is it that in each great class
some forms are far more highly developed than others? iWhy have
not the more highly developed forms everywhere supplanted and
exterminated the lower ? Lamarck, who believed in an innate and
inevitable tendency towards perfection in all organic beings, seems
to have felt this difficulty so strongly, that he was led to suppose
that new and simple forms are continually being produced by spon-
taneous generation. Science has not as yet proved the truth of
this belief, whatever the future may reveal. On our theory the
continued existence of lowly organisms offers no difficulty; for
natural selection, or the survival of the fittest, does not necessarily
include progressive development — it only takes advantage of such
variations as arise and are beneficial to each creature under its com-
plex relations of life. | And it may be asked what advantage, as far
as we can see, would it be to an infusorian animalcule — to an in-
testinal worm — or even to an earth-worm, to be highly organised.
If it were no advantage, these forms would be left, by natural selec-
tion, unimproved or but little improved, and might remain for
indefinite ages in their present lowly condition. And geology tells
us that some of the lowest forms, as the infusoria and rhizopods.

Chap, iV.j ORGANISATION TENDS TO ADVANCE. 99

have remained lor an enormous period in nearly their present state.
But to suppose that most of the many now existing low forms Lave
not in the least advanced since the first dawn of life would bo
extremely rash ; for every naturalist who has dissected seme of the
beings now ranked as very low in the scale, must have been struck
with their really wondrous and beautiful organisation.

Nearly the same remarks are applicable if we look to the different
grades of organisation within the same great group ; for instance,
in the vertebrata, to the co-existence of mammals and fish — amongst
mammalia, to the co-existence of man and the ornithorhynchus —
amongst fishes, to the co-existence of the shark and the lancelet
(Amphioxus), which latter fish in the extreme simplicity of its
structure approaches the invertebrate classes. But mammals and
fish hardly come into competition with each other ; the advance-
ment of the whole class of mammals, or of certain members in this
class, to the highest grade would not lead to their taking the place
of fishes. Physiologists believe that the brain must be bathed by
warm blood to be highly active, and this requires aerial respiration ;
so that warm-blooded mammals when inhabiting the water lie
under a disadvantage in having to come continually to the sur-
face to breathe. With fishes, members of the shark family would
not tend to supplant the lancelet ; for the lancelet, as I hear
from Fritz Miiller, has as sole companion and competitor on the
barren sandy shore of South Brazil, an anomalous annelid. The
three lowest orders of mammals, namely, marsupials, edentata, and
rodents, co-exist in South America in the same region with nume-
rous monkeys, and probably interfere little with each other.
.Although organisation, on the whole, may have advanced and be
still advancing throughout the world, yet the scale will always
present many degrees of perfection ; for the high advancement of
certain whole classes, or of certain members of each class, does not
at all necessarily lead to the extinction of those groups with which
they do not enter into close competition. In some cases, as we
'shall hereafter see, lowly organised forms appear to have been pre-
served to the present day, from inhabiting confined or peculiar
stations, where they have been subjected to less severe competitioii,
and where their scanty numbers have retarded the chance of favour-
able variations arising.

Finally, I believe that many lowly organised forms now exist
throughout the world, from various causes. In some cases varia-
tions or individual differences of a favourable natui'e may ne^^j:
have arisen for natural selection to act on and accumulate. In re
case, probably, has time sufficed for the utmost possible arrjoiurt oi.

H 2 3 >ii'

^00 CONVERGENCE OF CHARACTER. [Chap. IV

developmeiit. In some few cases there has been what we must call
retrogression of organisation. But the main cause lies in the fact
that under very simple conditions of life a high organisation would
be of no service, — possibly would be of actual disservice, as being
of a mere delicate nature, and more liable to be put out of order
and injured.

Looking to the first dawn of life, when all organic beings, as we
may believe, presented the simplest structure, how, it has been
asked, could the first steps in the advancement or differentiation of
parts have arisen? Mr. Herbert Spencer would probably answer
that, as soon as simple unicellular organism came by growth or
division to be compounded of several cells, or became attached to
any supporting surface, his law " that homologous units of any
order become differentiated in proportion as their relations to inci-
dent forces become different " would come into action. But as we
have no facts to guide us, speculation on the subject is almost useless.
It is, however, an error to suppose that there would be no struggle
for existence, and, consequently, no natural selection, until many
forms had been produced : variations in a single species inhabiting
an isolated station might be beneficial, and thus the whole mass of
individuals might be modified, or two distinct forms might arise.
But, as I remarked towards the close of the Introduction, no one
ought to feel surprise at much remaining as yet unexplained on the
origin of species, if we make due allowance for our profound igno-
rance on the mutual relations of the inhabitants of the world at the
present time, and still more so during past ages.

Convergence of Character.

Mr. H. C. Watson thinks that I have overrated the importance
of divergence of character (in which, however, he apparently
believes), and that convergence, as it may be called, has likewise
played a part. If two species, belonging to two distinct though
allied genera, had both produced a large number of new and diver-
gent forms, it is conceivable that these might approach each other
so closely that they would have all to be classed under the same
genus ; and thus the descendants of two distinct genera would con-
verge into one. But it would in most cases be extremely rash to attri-
bute to convergence a close and general similarity of structure in the
modified descendants of widely distinct forms. The shape of a crystal
is determined solely by the molecular forces, and it is not surprising
tlki'oidissimilar substances should sometimes assume the same form;
but with organic beings we should bear in mind that the form of

* C < < c

Chap. IV.] CONVERGENCE OF CHARACTER. 101

eacli depends on an infinitude of complex relations, namely on tha
variations which have arisen, these being due to causes far too
intricate to be followed out, — on the nature of the variations which
have been preserved or selected, and this depends on the surround-
ing physical conditions, and in a still higher degree on the sur-
rounding organisms with which each being has come into competi-
tion,— and lastly, on inheritance (in itself a fluctuatiog element) from
innumerable progenitors, all of which have had their forms Aeter-
mined through equally complex relations. It is incredible that the
descendants of two organisms, which had originally differed in a
marked manner, should ever afterwards converge so closely as to
lead to a near approach to identity throughout their whole organi-
sation. If this had occurred, we should meet with the same form,
independently of genetic connection, recurring in widely separated
geological formations ; and the balance of evidence is opposed to
any such an admission.

Mr. Watson has also objected that the continued action of natural
selection, together with divergence of character, would tend to make
an indefinite number of specific forms. As far as mere inorganic con-
ditions are concerned, it seems probable that a sufficient number of
species would soon become adapted to all considerable diversities
of heat, moisture, &c. ; but I fully admit that the mutual relations
of organic beings are more important ; and as the number o^ species
in any country goes on increasing, the organic conditions of life
must become more and more complex. Consequently there seems
at first sight no limit to the amount of profitable diversification of
structure, and therefore no limit to the number of species which
might be produced. We do not know that even the most prolific
area is fully stocked with specific forms : at the Cape of Good Hope
and in Australia, which support such an astonishing number of
species, many European plants have become naturalised. But
geology shows us, that from an early part of the tertiary period the
number of species of shells, and that from the middle part of this
same period the number of mammals, has not greatly or at all
increased. What then checks an indefinite increase in the number
of species? The amount of life (I do not mean the number of
specific forms) supported on an area must have a limit, depending
so largely as it does on physical conditions ; therefore, if an area be
inhabited by very man}'- species, each or nearly each I'pecies will be
represented by few individuals ; and such species will be liable to
extermination from accidental fluctuations in the nature of the
seasons or in the number of their enemies. The process of extermi-
nation in such cases would be rapid, whereas the production of new

102 NATURAL SELECTION. [Chap. lY

species must always be slow. Imagine the extreme case of as many
species as individuals in England, and the first severe winter or
very dry summer would exterminate thousands on thousands of
species. Rare species, and each species will become rare if the
number of species in any country becomes indefinitely increased,
will, on the principle often explained, present within a given period
few favourable variations ; consequently, the process of giving birth
to new specific forms would ,thus be retarded. When any species
becomes very rare, close interbreeding will help to exterminate it ;
authors have thought that this comes into play in accounting for
the deterioration of the Aurochs in Lithuania, of Eed Deer in Scot-
land, and of Bears in Norway, &c. Lastly, and this I am inclined
to think is the most important element, a dominant species, which
has already beaten many competitors in its own home, will tend to
spread and supplant many others. Alph. de CandoUe has shown
that those species which spread widely, tend generally to spread
very widely ; consequently, they will tend to supplant and exter-
minate several species in several areas, and thus check the inordinate
increase of specific forms throughout the world. Dr. Hooker has
recently shown that in the' S.E. corner of Australia, where, appa-
rently, there are many invaders from different quarters of the globe,
the endemic Australian species have been greatly reduced in number.
How much weight to attribute to these several considerations I
will not pretend to say ; but conjointly they must limit in each
country the tendency to an indefinite augmentation of specific
forms.

Summary of Chaj)ter.

C If under changing conditions of life organic beings present indivi-
I dual differences in almost every part of their structure, and this
i cannot be disputed ; if there be, owing to their geometrical rate of
,. increase, a severe straggle for life at some age, season, or year, and
this certainly cannot be disputed ; then, considering the infinite
. complexity of the relations of all organic beings to each other and to
\S I their conditions of life, causing an infinite diversity in structure, con-
stitution, and habits, to be advantageous to them, it would be a most
extraordinary fact if no variations had ever occurred useful to each
l)eing's own welfare, in the same manner as so many variations have
_occurred useful to man. But if variations useful to any organic
being ever do occur, assuredly individuals thus characterised will
have the best chance of being preserved in the struggle for life ;
and from the strong principle of inheritance, these will tend to
produce offspring similarly characterised. This principle of pre-

Chap. IV.] SL'MMAR^. 103

servation, or the survival of the fittest, I have called Natural
Selection. It le,ads-to the improvement of each creature in relation,
to its organic and inorganic conditions of life ; and consequently, in
most caseSj tqwhat_mu.st,l}e regarded as an advance in organisation.
Nevertheless, low and simple forms will long endure if well fitted for
their simple conditions of life. . — '

Natural selection, on the principle of qualities being inherited at
corresponding ages, can modify the egg, seed, or young, as easily
as the adult. Amongst many animals, sexual selection will have
given its aid to ordinary selection, by assuring to the most vigorous
and best adapted males the greatest number of offspring. Sexual
selection will also give characters useful to the males alone, in their
struggles or rivalry with other males ; and these characters will be
transmitted to one sex or to both sexes, according to the form of
inheritance which prevails.

Whether natural selection has really thus acted in adapting the
various forms of life to their several conditions and stations, must
be judged by the general tenor and balance of evidence given in the
following chapters. But we have already seen how it entails
extinction ; and how largely extinction has acted in the world's
history, geology plainly declares. Natural selection, also, leads to
divergence of character; for the more organic beings diverge in
structure, habits, and constitution, by so much the more can a large
number be supported on the same area, — of which we see proof by
looking to the inhabitants of any small spot, and to the productions
naturalised in foreign lands. Therefore, during the modification of
the descendants of any one species, and during the incessant struggle
of all species to increase in numbers, the more diversified the de-
scendants become, the better will be their chance of success in the
battle for life. Thus the small differences distinguishing varieties
of the same species, steadily tend to increase, till they equal the
greater differences between species of the same genus, or even of
distinct genera.

We have seen that it is the common, the widely-diffused, and
widely-ranging species, belonging to the larger genera within each
class, which vary most ; and these tend to transmit to their modified
offspring that superiority which now makes them dominant in
their own countries. Natural selection, as has just been remarked:
leads to divergence of character and to much extinction of the less
improved and intermediate forms of life. On these principles, the
nature of the affinities, and the generally well-defined distinctions
between the innumerable organic beings in each class throughout

104 NATURAL SELECTION [Chap IV.

the world, may be explained. It is a truly wonderful fact — tlie
wonder of which we are apt to overlook from familiarity — that all
animals and all plants throughout all time and spa££_sliould_be
related to each other in groups subordinate to groups^ in the manner
which we everywhere behold — namely, varieties of the same species
most closely related, species of the same genus less closely and
unequally related, forming sections and sub-genera, species of
distinct genera much less closely related, and genera related in
different degrees, forming sub-families, families, orders, sub-classes,
and classes. The several subordinate groups in any class cannot be
ranked in a single file, but seem clustered round points, and these
round other points, and so on in almost endless cycles. If species
had been independently created, no explanation would have been
possible of this kind of classification ; but it is explained through
inheritance and the complex action of natural selection, entailing
extinction and divergence of character, as we have seen illustrated
in the diagram.

The affinities of all the beings of the same class have sometimes
been represented by a great tree. I believe this simile largely
speaks the truth. The green and budding twigs may represent
sxisting species; and those produced during former years may
represent the long succession of extinct species. 'At each period of
growth all the growing twigs have tried to branch out on all sides,
and to overtop and kill the surrounding twigs and branches, in the
same manner as species and groups of species have at all times
overmastered other species in the great battle for life. The limbs
divided into great branches, and these into lesser and lesser branches,
were themselves once, when the tree was young, budding twigs.*
and this connection of the former and present buds by ramifying
branches may well represent the classification of all extinct and
living species in groups subordinate to groups. Of the many twigs
which flourished when the tree was a mere bush, only two or three,
now grown into great branches, yet survive and bear the other
branches ; so with the species which lived during long-past geolo-
gical periods, very few have left living and modified descendants^
["'From the first growth of the tree, many a limb and branch has
decayed and dropped off; and these fallen branches of various sizes
may represent those whole orders, families, and genera which have
now no living representatives, and which are known to us only in
a fossil state. As we here and there see a thin straggling branch
springing from a fork low down in a tree, and which by some
chance has been favoured and is still alive on its summit, so W6

Ceap. IV.l SUMMARY. 106

occasionally see an animal like the Ornithorhynchus or Lepidosiren,
which in some small degree connects by its affinities two large
branches of life, and which has apparently been saved from fatal
competition by having inhabited a protected station. As buds give
rise by growth to fresh buds, and these, if vigorous, branch out and
overtop on all sides many a feebler branch, so by generation I
believe it has been with the great Tree of Life, which fills with its
dead and broken branches the crust of the earth, and covers tho
surface with its ever-branching and beautiful ramifications.

106 LAWS OF VARIATION. [Chap. V

CHAPTEK V.

Laws of Variation.

Effects of changed conditions — Use and disuse, combined with natural
selection ; organs of flight and of vision — Acclimatisation — Correlated
variation — Compensation and economy of growth — False correlations
— Multiple, rudimentary, and lowly organised structures variable —
Parts developed in an unusual manner are highly variable : specific
characters more variable than generic: secondary sexual characters
variable — Species of the same genus vary in an analogous manner —
Reversions to long-lost characters — Summary.

I HAVE hitherto sometimes spoken as if the variations — so common
and multiform with organic beings under domestication, and in a
lesser degree with those under nature — were due to chance. This,
of course, is a wholly incorrect expression, but it serves to acknow-
ledge plainly our ignorance of the cause of each pariiciilar variaHon.
Some authors believe it to be as much the function of the repro-
(||;fiti2e_system to produce individual differences, or slight devfatiohs
of structureT'as to make the child like its i^arents. But the fact of
variations and monstrosities occurring much more frequently under
domestication than under nature, and the greater variability of species
having wide ranges than of those with restricted ranges, lead to
the conclusion that variability is generally related to the condi-
tions of life to which each species has been exposed during several
successive generations. In the first chapter I attempted to show that
changed conditions act in two ways, directly on the whole organisa=;_
tion or on certain parts alone, and indirectly through the reproductive
system. In all cases there are two factors, the nature of the
organism, which is much the most important of the two, and the
nature of the conditions. The direct action of changed conditions
leads to definite or indefinite results. In the latter case the organi-
sation seems to becopie plastic, and we have much fluctuating vari-
ability. In the former case the nature of the organism is such
tliat it yields readily, when subjected to certain conditions, and all,
or nearly all the individuals become modified in the same way.

It is very difficult to decide how far changed conditions, such as
of climate, food, &c., have acted in a definite manner. There is

CUAP. V.l LAWS OF VARIATION. 107

reason to believe that in the course of time the effects have "been
greater than can be proved by clear evidence. But we may safely
conclude that the innumerable complex co-adaptations of structure,
which ■we see throughout nature between various organic beings,
cannot be attributed simply to such action. In the following cases
the conditions seem to have produced some slight definite effect : E.
Forbes asserts that shells at their southern limit, and when living in
shallow water, are more bri'ghtly coloured than those of the same
species from further north or from a greater depth ; but this
certainly does not always hold good. Mr. Gould believes that birds
of the same species are more brightly coloured under a clear atmos-
phere, than when living near the coast or on islands ; and Wollaston
is convinced that residence near the sea affects the colours of insects.
Moquin-Tandon gives a list of plants which, when growing near the
sea-shore, have their leaves in some degree fleshy, though not else-
where fleshy. These slightly varying organisms are interesting in
as far as they present characters analogous to those possessed by the
species which are confined to similar conditions.

When a variation is of the slightest use to any being, we cannot tell
how much to attribute to the accumulative action of natural selection,
and how much to the definite action of the conditions of life. Thus,
it is well known to furriers that animals of the same species have
thicker and better fur the further north they live ; but who can tell
how much of this difference may be due to the warmest-clad indivi-
duals having been favoured and preserved during many generations,
and how much to the action of the severe climate ? for it would
appear that climate has some direct action on the hair of our domes-
tic quadrupeds.

Instances could be given of similar varieties being produced from
the same species under external conditions of life as different as can
well be conceived ; and, on the other hand, of dissimilar varieties
being produced under apparently the same external conditions.
Again, innumerable instances are known to every naturalist, of
species keeping true, or not varying at all, although living under
the most opposite climates. Such considerations as these incline me
to lay less weight on the direct action of the surrounding con-
ditions, than on a tendency to vary, due to causes of which we are
quite ignorant.

In one sense the conditions of life may be said, not only to cause
variability, either directly or indirectly, but likewise to include
natural selection ; for the conditions determine whether this or that
variety shall survive. But when man is the selecting agent, we
clearly see that the two elements of change are distinct ; variability

108 EFFECTS OF USE AND DISUSE. [Chap. V

is in some manner excited, but it is the will of man wliicli aocumu-
lates the variations in certain directions ; and it is this latter agency
which answers to the survival of the fittest under nature.

Effects of the increased Use and Disuse of PartSy as contrdled
hy Natural Selection.

From the facts alluded to in the first chapter, I think there can
be no doubt that use in our domestic animals has strengthened
and enlarged certain parts, and disu-se diminished them ; and that
such modifications are inherited. Under free nature, we have no
standard of comparison, by which to judge of the effects of long-
continued use or disuse, for we know not the parent-forms ; but
many animals possess structures which can be best explained by
the effects of disuse. As Professor Owen has remarked, there is no
greater anomaly in nature than a bird that cannot fly ; yet there are
several in this state. The logger-headed duck of South America
can only flap along the surface of the water, and has its wings in
nearly the same condition as the domestic Aylesbury duck : it is a
remarkable fact that the young birds, according to Mr. Cunning-
ham, can fly, while the adults have lost this power. As the larger
ground-feeding birds seldom take flight except to escape danger, it
is probable that the nearly wingless condition of several birds, now
inhabiting or which lately inhabited several oceanic islands, tenanted
by no beast of prey, has been caused by disuse. The ostrich indeed
inhabits continents, and is exposed to danger from which it cannot
escape by flight, but it can defend itself by kicking its enemies, as
efficiently as many quadrupeds. We may believe that the proge-
nitor of the ostrich genus had habits like those of the bustard, and
that, as the size and weight of its body were increased during suc-
cessive generations, its legs were used more, and its wings less;
until they became incapable of flight.

Kirby has remarked (and I have observed the same fact) that the
anterior tarsi, or feet, of many male dung-feeding beetles are often
broken off ; he examined seventeen specimens in his own collection,
and not one had even a relic left. In the Onites apelles the tai*si
are so habitually lost, that the insect has been described as not
having them. In some other genera they are present, but in a
rudimentary condition. In the Ateuchus or sacred beetle of the
Egyptians, they are totally deficient. The evidence that accidental
mutilations can be inherited is at present not decisive ; but the
remarkable cases observed by Brown-S^quard in guinea-pigs, of the
inherited effects of operations, should make us cautious in denying

Chap. V.J EFFECTS OF USE AND DISUSE. 101

this tendency. Hence it will perhaps be safest to look at the entire
absence of the anterior tarsi in Ateuchus, and their rudimentary
condition in some other genera, not as cases of inherited mutilations,
but as due to the effects of long-continued disuse ; for as many
dmig-feeding beetles are generally found with their tarsi lost, this
ninst happen early in life ; therefore the tarsi cannot be of much
importance or be much used by these insects.

In some cases we might easily put down to disuse modifications
of structure which are wholly, or mainly, due to natural selection.
Mr. Wollaston has discovered the remarkable fact that 200 beetles.
OTit of the 550 species (but more are now known) inhabiting
Madeira, are so far deficient in wings that they cannot fly; and
that, of the twenty-nine endemic genera, no less than twenty- three
have all their species in this condition! Several facts, — namely,
that beetles in many parts of the world are frequently blown to sea
and perish ; that the beetles in Madeira, as observed by Mr.
"Wollaston, lie much concealed, until the wind lulls and the sun
shines; that the proportion of wingless beetles is largei on the
exposed Desertas than in Madeira itself ; and especially the extra-
ordinary fact, so strongly insisted on by Mr. Woilaston, that certain
large groups of beetles, elsewhere excessively numerous, which
absolutely require the use of their wings, are here almost entirely
absent; — these several considerations make me believe that the
wingless condition of so many Madeira beetles is mainly due to
the action of natural selection, combined probably with disuse. For
during many successive generations each individual beetle which
flew least, either from its wings having been ever so little less perfectly
developed or from indolent habit, will have had the best chance of
surviving from not being blown out to sea ; and, on the other hand,
those beetles which most readily took to flight would oftenest have
been blown to sea, and thus destroyed.

The insects in Madeira which are not ground-feeders, and which,
as certain flower-feeding coleoptera and lepidoptera, must habitually
use their wings to gain their subsistence, have, as Mr. Wollaston
suspects, their wings not at all reduced, but even enlarged. This is
quite compatible with the action of natural selection. For when a
new insect first arrived on the island, the tendency of natural
selection to enlarge or to reduce the wings, would depend on
whether a greater number of individuals were saved by successfully
battling with the winds, or by giving up the attempt and rarely or
never flying. As with mariners shipwrecked near a coast, it would
have been better for the good swimmers if they had been able to
swim still further, whereas it would have been better for the bad

1 1 0 EFFECTS OF USE AND DISUS£. [Chap. V

swimmers if they had not been able to swim at all and had stuck
to the wreck.

The eyes of moles and of some burrowing rodents are rudimentary
in size, and in some cases are quite covered by skin and fur. This
state of the eyes is probably due to gradual reduction from disuse,
but aided perhaps by natural selection. In South America, a bur-
rowing rodent, the tuco-tuco, or Ctenomys, is even more subter-
ranean in its habits than the mole ; and I was assured by a
Spaniard, who had often caught them, that they were frequently
blind. One which I kept alive was certainly in this condition, the
cause, as appeared on dissection, having been inflammation of the
nictitating membrane. As frequent inflammation of the eyes must
be injurious to any animal, and as eyes are certainly not necessary
to animals having subterranean habits, a reduction in their size,
with the adhesion of the eyelids and growth of fur over them,
might in such case be an advantage ; and if so, natural selection
would aid the effects of disuse.

It is well known that several animals, belonging to the most
different classes, which inhabit the caves of Carniola and of Ken-
tucky, are blind. In some of the crabs the foot-stalk for the eye
remains, though the eye is gone ; — the stand for the telescope is
there, though the telescope with its glasses has been lost. As it is
difficult to imagine that eyes, though useless, could be in any way
injurious to animals living in darkness, their loss may be attributed
to disuse. In one of the blind animals, namely, the cave-rat
(Neotoma), two of which were captured by Professor Silliman at
above half a mile distance from the mouth of the cave, and there-
fore not in the profoundest depths, the eyes were lustrous and ol
large size ; and these animals, as I am informed by Professor Silli-
man, after having been exposed for about a month to a graduated
light, acquired a dim perception of objects.

It is difficult to imagine conditions of life more similar than
deep limestone caverns under a nearly similar climate ; so that, in
accordance with the old view of the blind animals having been
separately created for the American and European caverns, very
close similarity in their organisation and affinities might have been
expected. This is certainly not the case if we look at the two
whole faunas ; and with respect to the insects alone, Schiodte has
remarked, " We are accordingly prevented from considering the
entire phenomenon in any other light than something purely local,
and the similarity which is exhibited in a few forms between the
Mammoth cave (in Kentucky) and the caves in Carniola, otherwise
than as a very plain expression of that analogy which sulosista

Chap. V.] EFFECTS CF USE AND DISUSE. Ill

generally between the fauna of Europe and of North America."
On my view we must suppose that American animals, having in
most cases ordinary powers of vision, slowly migrated by successive
generations from the outer world into the deeper and deeper re-
cesses of the Kentucky caves, as did European animals into the
caves of Europe. We have some evidence of this gradation of
habit ; for, as Schiodte remarks, " We accordingly look upon the
subterranean faunas as small ramifications which have penetrated
into the earth from the geographically limited faunas of the adja-
cent tracts, and which, as they extended themselves into darkness,
have been accommodated to surrounding circumstances. Animals
not far remote from ordinary forms, prepare the transition from
light to darkness. Next follow those that are constructed for twi-
light ; and, last of all, those destined for total darkness, and whose
formation is quite peculiar." These remarks of Schiodte's, it should
be understood, apply not to the same, but to distinct species. By
the time that an animal had reached, after numberless generations,
the deepest recesses, disuse will on this view have more or less
perfectly obliterated its eyes, and natural selection will often have
effected other changes, such as an increase in the length of the
antennae or palpi, as a compensation for blindness. Notwithstand-
ing such modifications, we might expect still to see in the cave-
animals of America, affinities to the other inhabitants of that con-
tinent, and in those of Europe to the inhabitants of the European
continent. And this is the case with some of the American cave-
animals, as I hear from Professor Dana ; and some of the European
cave-insects are very closely allied to those of the surrounding
country. It would be difficult to give any rational explanation of
Ihe affinities of the blind cave-animals to the other inhabitants
of the two continents on the ordinary view of their independent
creation. That several of the inhabitants of the caves of the Old
and New Worlds should be closely related, we might expect from
the well-known relationship of most of their other productions. As
a blind species of Bathyscia is found in abundance on shady rocks
far from caves, the loss of vision in the cave-species of this one
genus has probably had no relation to its dark habitation ; for it
is natural that an insect already deprived of vision should readily
become adapted to dark caverns. Another blind genus (Anoph-
thalmus) offers this remarkable peculiarity, that the species, as
Mr. Murray observes, have not as yet been found anywhere except
in caves ; yet those which inhabit the several caves of Europe and
America are distinct ; but it is possible that the progenitors of these
several species, whilst they were furnished with eyes, may formerly

112 ACCLIMATISATipN. [Chap. V

r

have ranged over both continents, and then have become extinct,
excepting in their present secluded abodes. Far from feeling sur-
prise that some of the cave-animals should be very anomalous, as
Agassiz has remarked in regard to the blind fish, the Amblyopsis,
and as is the case with the blind Proteus with reference to the
reptiles of Europe, I am only surprised that more wrecks of ancient
life have not been preserved, owing to the less severe competition to
which the scanty inhabitants of these dark abodes will have been
exposed.

Acclimatisation.

Habit is hereditary with plants, as in the period of flowering, in
the time of sleep, in the amount of rain requisite for seeds to germi-
nate, &c., and this leads me to say a few words on acclimatisation.
As it is extremely common for distinct species belonging to the same
genus to inhabit hot and cold countries, if it be true that all the
species of the same genus are descended from a single parent-form,
acclimatisation must be readily effected during a long course of
descent. It is notorious that each species is adapted to the climate
of its ov/n home : species from an arctic or even from a temperate
region cannot endure a tropical climate, or conversely. So again,
many succulent plants cannot endure a damp climate. But the
degree of adaptation of species to the climates under which they
live is often overi-ated. We may infer this from our frequent in-
ability to predict whether or not an imported plant will endure our
climate, and from the number of plants and animals brought from
different countries which are here perfectly healthy. We have
reason to believe that species in a state of nature are closely limited
in their ranges by the competition of other organic beings quite as
much as, or more than, by adaptation to particular climates. But
whether or not this adaptation is in most cases very close, we have
evidence with some few plants, of their becoming, to a certain
extent, natm'ally habituated to different temperatures ; that is, they
become acclimatised : thus the pines and rhododendrons, raised from
seed collected by Dr. Hooker from the same species growing at
different heights on the Himalaya, were found to possess in this
country different constitutional powers of resisting cold. Mr.
Thwaites informs me that he has observed similar facts in Ceylon 5
analogous observations have been made by Mr. H. C. Watson on
European species of plants brought from the Azores to England :
and I could give other cases. In regard to animals, several authentic
instances could be adduced of species having largely extended,
within historical times, their range from warmer to cooler latitudes,

Char /.] ACCLIMATISATION. 113

and conversely ; but v;e do not positively know that these ':«,iumais
were strictly adapted to their native climate, though in all orcinary
cases we assume such to be the case ; nor do we know th^t the^
have subsequently become specially acclimatised to their new
homes, so as to be better fitted for them than they were at first.

As we may infer that our domestic animals were originally chosen
by uncivilised man because they were useful and because they bred
readily under confinement, and not because they were subsequently
found capable of far-extended transportation, the common and ex-
traordinary capacity in our domestic animals of not only withstand-
ing the most different climates, but of being perfectly fertile (a far
severer test) under them, may be used as an argument that a large
proportion of other animals now in a state of nature could easily
be brought to bear widely different climates. We must not, how-
ever, push the foregoing argument too far, on account of the pro-
bable origin of some of our domestic animals from several wild
stocks ; the blood, for instance, of a tropical and arctic wolf may
perhaps be mingled in our domestic breeds. The rat and mouse
cannot be considered as domestic animals, but they have been trans-
ported by man to many parts of the world, and now have a far
wider range than any other rodent ; for they live under the cold
climate of Faroe in the north and of the Falklands in the south,
and on many an island in the torrid zones. Hence adaptation to
any special climate may be looked at as a quality readily grafted on
an innate wide flexibility of constitution, common to most animals.
CJn~this view, the capacity of enduring the most different climates
by man himself and by his domestic animals, and the fact of the
extinct elephant and rhinoceros having formerly endured a glacial
climate, whereas the living species are now all tropical or sub-
tropical in their habits, ought not to be looked at as anomalies, but
as examples of a very common flexibility of constitution, brought,
under peculiar circumstances, into action.

How much of the acclimatisation of species to any peculiar
climate is due to mere habit, and how much to the natural selection
of varieties having different innate constitutions, and how much to
both means combined, is an obscure question. That habit or custom
has some influence, I must believe, both from analogy and from the
incessant advice given in agricultural works, even in the ancient
Encyclopoedias of China, to be very cautious in transporting ani-
mals from one district to another. And as it is not likely that man
should have succeeded in selecting so many breeds and sub-breeds
with constitutions specially fitted for their own districts, the result
must, I think, be due to habit. On the other hand, natural selec-

114 CORRELATED VARIATION. [Chap. V,

tion would inevitably tend to preserve those individuals which, were
born with constitutions best adapted to any country which they
inhabited. In treatises on many kinds of cultivated plants, certain
varieties are said to withstand certain climates better than others ;
this is strikingly shown in works on fruit-trees published in the
United States, in which certain varieties are habitually recom-
mended for the northern and others for the southern States ; and as
most of these varieties are of recent origin, they cannot ov/e their
constitutional differences to habit. The case of the Jerusalem
artichoke, which is never propagated in England by seed, and of
which consequently new varieties have not been produced, has even
been advanced, as proving that acclimatisation cannot be effected,
for it is now as tender as ever it was ! The case, also, of the kidney-
bean has been often cited for a similar purpose, and with much
greater weight; but until some one will sow, during a score of
generations, his kidney-beans so early that a very large proportion
are destroyed by frost, and then collect seed from the few survivors,
with care to prevent accidental crosses, and then again get seed
from these seedlings, with the same precautions, the experiment
cannot be said to have been tried. Nor let it be supposed that
differences in the constitution of seedling kidney-beans never
appear, for an account has been published how much more hardy
some seedlings are than others ; and of this fact I have myself
observed striking instances.

On the whole, we may conclude that habit, or use and disuse,
have, in some cases, played a considerable part in the modification
of the constitution and structure ; but that the effects have often
been largely combined with, and sometimes overmastered by, the
natural selection of innate variations.

Correlated Variation.

I mean by this expression that the whole organisation is so tied
together during its growth and development, that when slight
variations in any one part occur, and are accumulated through
natural selection, other parts become modified. This is a very im-
portant subject, mosFimpeTTectly understood, and no doubt wholly
different classes of facts may be here easily confounded together.
We shall presently see that simple inheritance often gives the false
appearance of correlation. One of the most obvious real cases is,
that variations of structure arising in the young or larvae naturally
tend to affect the structure of the mature animal. The several
parts of the body which are homologous, and which, at an early
embryonic period, are identical in structure, and which are necss-

Chap. V,] CORRELATED VARIATION. 115

Barily exposed to similar conditions, seem eminently liable to vary
in a like manner : we see this in the right and left sides of the
body varying in the same manner ; in the front and hind legs, and
even in the jaws and limbs, varying together, for the lower jaw
is believed by some anatomists to be homologous with the limbs.
These tendencies, I do not doubt, may be mastered more or less
completely by natural selection : thus a family of stags once existed
with an antler only on one side ; and if this had been of any great
use to the breed, it might probably have been rendered permanent
by selection.

Homologous parts, as has been remarked by some authors, tend
to cohere ; this is often seen in monstrous plants : and nothing
is more common than the union of homologous parts in normal
structures, as in the union of the petals into a tube. Hard parts
seem to affect the form of adjoining soft parts ; it is believed by
some authors that with birds the diversity in the shape of the
pelvis causes the remarkable diversity in the shape of their kidneys.
Others believe that the shape of the pelvis in the human mother
influences by pressure the shape of the head of the child. In
snakes, according to Schlegel, the form of the body and the manner
of swallowing determine the position and form of several of the
most important viscera.

The nature of the bond is frequently quite obscure. M. Is.
Geoffroy St. Hilaire has forcibly remarked, that certain malcon-
formations frequently, and that others rarely, co-exist, without our
being able to assign any reason. What can be more singular than
the relation in cats between complete whiteness and blue eyes with
deafness, or between the tortoise-shell colour and the female sex ;
or in pigeons between their feathered feet and skin betwixt the outer
toes, or between the presence of more or less down on the young
pigeon when first hatched, with the future colour of its plumage :
or, again, the relation between the hair and teeth in the naked
Turkish dog, though here no doubt homology comes into play?
With respect to this latter case of correlation, I think it can hardly
be accidental, that the two orders of mammals which are most
abnormal in their dermal covering, viz., Cetacea (whales) and
Edentata (armadilloes, scaly ant-eaters, &c.), are likewise on the
v/hole the most abnormal in their teeth ; but there are so many
exceptions to this rule, as Mr. Mivart has remarked, that it has
little value.

I know of no case better adapted to show the importance of the
laws of correlation and variation, independently of utility and
therefore of natural selection, than that of the difference between

I 2

116 CORRELATED VARIATION. [Chap. V.

the outer and inner flowers in some Compositous and Umbellifei-ous
plants. Every one is familiar with the difference between the ray
and central florets of, for instance, the daisy, and this difference is
often accompanied with the partial or- complete abortion of the
reproductive organs. But in some of these plants, the seeds also
differ in shape and sculpture. These differences have sometimes
been attributed to the pressure of the involucra on the florets, or
to their mutual pressure, and the shape of the seeds in the ray-
florets of some Compositce countenances this idea ; but with the
Umbellifer^e, it is by no means, as Dr. Hooker informs me, the
species with the densest heads which most frequently differ in
their inner and outer flowers. It might have been thought that
the development of the ray-petals by drawing nourishment from the
reproductive organs causes their abortion ; but this can hardly be
the sole cause, for in some Compositse the seeds of the outer and
inner florets differ, without any difference in the corolla. Possibly
these several differences may be connected with the different flow
of nutriment towards the central and external flowers : we know,
at least, that with irregular flowers, those nearest to the axis arc
most subject to peloria, that is to become abnormally symmetrical.
I may add, as an instance of this fact, and as a striking case of
correlation, that in many pelargoniums, the two upper petals in
the central flower of the truss often lose their patches of darker
colour ; and when this occurs, the adherent nectary is quite aborted ;
the central flower thus becoming peloric or regular. When the
colour is absent from only one of the two upper petals, the nectary
is not quite aborted but is much shortened.

With respect to the development of the corolla, Sprengel's idea
that the ray-florets serve to attract insects, whose agency is highly
advantageous or necessary for the fertilisation of these plants, is
highly probable ; and if so, natural selection may have come into play.
But with respect to the seeds, it seems impossible that their differ-
ences in shape, which are not always correlated with any difference
in the corolla, can be in any way beneficial : yet in the Umbelli-
fer£e these differences are of such apparent importance — the seeds
being sometimes orthospermous in the exterior flowers and coelo-
spermous in the central flowers, — that the elder De Candolle
founded his main divisions in the order on such characters. Hence
modifications of structure, viewed by systematists as of high value,
may be wholly due to the laws of variation and correlation, without
being, as far as we can jticlge, of the slightest service to the species.

We may often falsely attribute to correlated variation structures
which are common to whole groups of species, and which in tmlh

Ckap. v.] COMPENSATION AND ECONOMY OF GROWTH. 117

arc simply due to inheritance ; for an ancient progenitor may have
acquired through natural selection some one modification in struc-
ture, and, after thousands of generations, some other and inde-
pendent modification ; and these two modifications, having been
transmitted to a whole group of descendants with diverse habits,
would naturally be thought to be in some necessary manner cor-
related. Some other correlations are apparently due to the manner
in which natural selection can alone act. For instance, Alph. de
Candolle has remarked that winged seeds are never found in fruits
which do not open : I should explain this rule by the impossibility
of seeds gradually becoming winged through natural selection, unless
the capsules were open ; for in this case alone could the seeds, which
were a little better adapted to be wafted by the wind, gain an
advantage over others less well fitted for wide dispersal.

Compensation and Economy of Growth.

The elder Geoffrey and Goethe propounded, at about the same time
their law of compensation or balancement of growth ; or, as Goethe
expressed it, " in order to spend on one side, nature is forced to
economise on the other side." I think this holds true to a certain
extent with our domestic productions : if nourishment flows to one
part or organ in excess, it rarely flows, at least in excess, to another
part ; thus it is difficult to get a cow to give much milk and to
fatten readily. The same varieties of the cabbage do not yield
abundant and nutritious foliage and a copious supply of oil-bearing
seeds. When the seeds in our fruits become atrophied, the fruit
itself gains largely in size and quality. In our poultry, a large
tuft of feathers on the head is generally accompanied by a diminished
comb, and a large beard by diminished wattles. With species in
a state of nature it can hardly be maintained that the law is of
universal application; but many good observers, more especially
botanists, believe in its truth. I will not, however, here give any
instances, for I see hardly any way of distinguishing between tho
effects, on the one hand, of a part being largely developed through
natural selection and another and adjoining part being reduced by
ihis same process or by disuse, and, on the other hand, the actual
withdrawal of nutriment from one part owing to the excess of
growth in another and adjoining part.

I suspect, also, that some of the cases of compensation which
have been advanced, and likewise some other facts, may be merged
under a more general principle, namely, that natural selection is
continually trying to economise every part of the organisation. If
under changed conditions of life a structure, before useful, becomes

118 MULTIPLE AND RUDIMENTARY [Chap. V

less useful, its diminution will be favoured, for it will_grofit tho__
individual nofto^ave . lts_ jiutriment wasted in building-up an
useless structure. I can thus only understand a fact with which
I was much struck when examining cirripedes, and of which many-
analogous instances could be given: namely, that when a cirripede is
parasitic within another cirripede and is thus protected, it loses more
or less completely its own shell or carapace. This is the case with
the male Ibla, and in a truly extraordinary manner with the Proteo-
lepas : for the carapace in all other cirripedes consists of the three
highly-important anterior segments of the head enormously deve-
loped, and furnished with great nerves and muscles; but in the
parasitic and protected Proteolepas, the whole anterior part ot
the head is reduced to the merest rudiment attached to the bases
of the prehensile antennae. Now the saving of a large and complex
structure, when rendered superfluous, would be a decided advantage
to each successive individual of the species ; for in the struggle for
life to which every animal is exposed, each would have a better
chance of supporting itself, by less nutriment being wasted.

Thus, as I believe, natural selection will tend in the long run to
reduce any part of the organisation, as soon as it becomes, through
changed habits, superfluous, without by any means causing some
nther part to be largely developed in a corresponding degree. And,
£onversely, that natural selection may perfectly well succeed in
largely developing an organ without requiring as a necessary com-
pensation the reduction of some adjoining part.

Multiple, Rudimentary, and Lowly-organised Structures are

Variable.

It seems to be a rule, as remarked by Is. Geoffroy St. Hilaire,
both with varieties and species, that when any part or organ is
repeated many times in the same individual (as the vertebras in
snakes, and the stamens in polyandrous flowers) the number is
variable ; whereas the same part or organ, when it occurs in lesser
numbers, is constant. The same author as well as some botanists
have further remarked that multiple parts are extremely liable to
vary in structure. As " vegetative repetition," to use Prof. Owen's
expression, is a sign of low organisation, the foregoing statements
accord with the common opinion of naturalists, that beings which
stand low in the scale of nature are more variable than those which
are higher. I presume that lowness here means that the several
parts of the organisation have been but little specialised for particular
functions ; and as long as the same part has to perform diversified
work, we can perhaps see why it should remain variable, that is,

CHAr. v.] STEUCTURES VARIABLE. 119

why natural selection should not lave preserved or rejected each
little deviation of form so carefully as when the part has to serve
for some one special purpose. In the same way that a knife which
has to cut all sorts of things may be of almost any shape ; whilst
a tool for some particular purpose must be of some particular
chape. Natural selection, it should never be forgotten, can act
solely thi'ough and for the advantage of each being.

Kudimentary parts, as it is generally admitted, are apt to be
highly variable. We shall have to recur to this subject ; and I will
nere only add that their variability seems to result from their use-
lessness, and consequently from natural selection having had no
power to check deviations in their structure.

JL Part developed in any Species in an extrawdinary degree or
manner^ in comparison with the same Fart in allied Species^
tends to be highly variable.

Several years ago I was much struck by a remark, to the above
effect, made by Mr. Watorhouse. Professor Owen, also, seems to
have come to a nearly similar conclusion. It is hopeless to attempt
to convince any one of the truth of the above proposition without
giving the long array of facts which I have collected, and which
cannot possibly be here introduced. I can only state my conviction
that it is a rule of high generality. I am aware of several causes of
error, but I hope that I have made due allowance for them. It
should be understood that the rule by no means applies to any
part, however unusually developed, unless it be unusually developed
in. one species or in a few species in comparison with the same part
in many closely allied species. Thus, the wing of a bat is a most
abnormal structure in the class of mammals ; but the rule would
not apply here, because the whole group of bats possesses wings ; it
would apply only if some one species had wings developed in a
remarkable manner in comparison with the other species of the
same genus. The rule applies very strongly in the case of secondary
sexual characters, when displayed in any unusual manner. The term,
secondary sexual characters, used by Hunter, relates to characters
which are attached to one sex, but are not directly connected with the
act of reproduction. The rule applies to males and females ; but more
rarely to the females, as they seldom offer remarkable secondary sexual
characters. The rule being so plainly applicable in the case of secondary
sexual characters, may be due to the great variability of these charac-
ters, whether or not displayed in any unusual manner — of which fact 1
tliink there can be little doubt. But that our rule is not confined
to secondary sexual characters is clearly shown in the casa of

120 UNUSUALLY DEVELOPED PARTS HIGHLY VARIABLE. [Chap. V.

liermaplirodite cirripedes ; I particularly attended to Mr. Water-
house's remark, whilst investigating this Order, and I am fully con-
vinced that the rule almost always holds good. I shall, in a future
work, give a list of all the more remarkable cases ; I will here give
only one, as it illustrates the rule in its largest application. The
opercular valves of sessile cirripedes (rock barnacles) arc, in every
sense of the word, very important structures, and they differ
extremely little even in distinct genera ; but in the several species
of one genus, Pyrgoma, these valves present a marvellous amount
of diversification ; the homologous valves in the different specie^
being sometimes wholly unlike in shape ; and the amount of varia-
tion in the individuals of the same species is so great, that it is no
exaggeration to state that the varieties of the same species differ
more from each other in the characters derived from these impor-
tant organs, than do the species belonging to other distinct genera.

As with birds the individuals of the same species, inhabiting the
same country, vary extremely little, I have particularly attended to
them ; and the rule certainly seems to hold good in this class. I
cannot make out that it applies to plants, and this would have
seriously shaken my belief in its truth, had not the great vari-
ability in plants made it particularly difficult to compare their
relative degrees of variability.

When we see any part or organ developed in a remarkable degree
or manner in a species, the fair presumption is that it is of high
importance to that species ; nevertheless it is in this case eminently
liable to variation. Why should this be so ? On the view that
each species has been independently created, with all its parts as
we now see them, I can see no explanation. But on the view that
groups of species are descended from some other species, and have
been modified through natural selection, I think we can obtain
some light. First let me make some jDreliminary remarks. If, in
our domestic animals, any part or the whole animal be neglected,
and no selection be applied, that part (for instance, the comb in the
Dorking fowl) or the whole breed will cease to have a uniform
character ; and the breed may be said to be degenerating. In
rudimentary organs, and in those which have been but little
specialised for any particular purpose, and perhaps in polymorphic
groups, we see a nearly parallel case ; for in such cases natural selec-
tion either has not or cannot have come into full play, and thus the
organisation is left in a fluctuating condition. But what here more
particularly concerns us is, that those points in our domestic
animals, which at the present time are undergoing rapid change by
continued selection, are also eminently liable to variation. Look at

Chap. V.] UNUSUALLY DEVELOPED PARTS HIGHLY VARIABLE. 121

the individuals of the same breed of the pigeon, and see what a
prodigious amount of difference there is in the beaks of tumblers, in
the beaks and wattle of carriers, in the carriage and tail of fan tails,
&c., these being the points now mainly attended to by English
fanciers. Even in the same sub-breed, as in that of the short-faced
tumbler, it is notoriously difiScult to breed nearly perfect birds,
many departing widely from the standard. There may truly be
said to be a constant struggle going on between, on the one hand
the tendency to reversion to a less perfect state, as well as an innate
tendency to new variations, and, on the other hand, the power ol
steady selection to keep the breed true. In the long run selection
gains the day, and we do not expect to fail so completely as to breed
bird as coarse as a common tumbler pigeon from a good short-faced
strain. But as long as selection is rapidly going on, much variability
in the parts undergoing modification may always be expected.

Now let us turn to nature. When a part has been developed in
an extraordinary manner in any one species, compared with the
other species of the same genus, we may conclude that this part has
undergone an extraordinary amount of modification since the period
when the several species branched off from the common progenitor
of the genus. This period will seldom be remote in any extreme
degree, as species rarely endure for more than one geological period.
An extraordinary amount of modification implies an unusually
large and long-continued amount of variability, which has con-
tinually been accumulated by natural selection for the benefit of
the species. But as the variability of the extraordinarily developed
part or organ has been so great and long-continued within a period
not excessively remote, we might, as a general rule, still expect to
find more variability in such parts than in other parts of the
organisation which have remained for a much longer period nearly
constant. And this, I am convinced, is the case. That the struggle
between natural selection on the one hand, and the tendency to
reversion and variability on the other hand, will in the course of
time cease ; and that the most abnormally developed organs may be
made constant, I see no reason to doubt. Hence, when an organ,
however abnormal it may be, has been transmitted in approximately
the same condition to many modified descendants, as in the case of
the wing of the bat, it must have existed, according to our theory,
for an immense period in nearly the same state ; and thus it has
come not to be more variable than any other structure. It is only
in those cases in which the modification has been comparatively
recent and extraordinarily great that we ought to find the generative
variability J as it may be called, still present in a high degree. For

122 SPECIFIC CHARACTERS [Chap. V.

in this case the variability will seldom as yet have "been fixed by
the continued selection of the individuals varying in the required
manner and degree, and by the continued rejection of those tending
to revert to a former and less-modified condition.

Specific Characters more Variable than Generic Characters.

The principle discussed under the last heading may be applied to
our present subject. It is notorious that specific characters are
more variable than generic. To explain by a simple example what
is meant : if in a large genus of plants some species had blue
flowers and some had red, the colour would be only a specific
character, and no one would be surprised at one of the blue species
varying into red, or conversely ; but if all the species had blue
flowers, the colour would become a gen-eric character, and its varia-
tion would be a more unusual circumstance. I have chosen this
example because the explanation which most naturalists would
advance is not here applicable, namely, that specific characters are
more variable than generic, because they are taken from parts of less
physiological importance than those commonly used for classing
genera, I believe this explanation is partly, yet only indirectly,
true; I shall, however, have to return to this point in the chapter
on Classification. It would be almost superfluous to adduce evidence
in support of the statement, that ordinary specific characters are
more variable than generic ; but with respect to important charac-
ters, I have repeatedly noticed in works on natural history, that
when an author remarks with surprise that some important organ
or part, which is generally very constant throughout a large group
of species, differs considerably in closely-allied species, it is often
variable in the individuals of the same species. And this fact shows
that a character, which is generally of generic value, when it sinks
in value and becomes only of specific value, often becomes variable,
though its physiological importance may remain the same. Some-
thing of the same kind applies to monstrosities : at least Is. Geofiroy
St. Hilaire apparently entertains no doubt, that the more an organ
normally differs in the different species of the same group, the more
subject it is to anomalies in the individuals.

On the ordinary view of each species having been independently
created, why should that part of the structure, which difi"ers from
the same part in other independently-created species of the same
genus, be more variable than those parts which are closely alike in
the several species? I do not see that any explanation can be
given. But on the view that species are only strongly marked and
fixed varisties, we might expect often to find them still continuing

Chap. V.] MORE VARIABLE THAN GENERIC. 123

to vary in those parts of their structure which have varied within a
niDderately recent period, and which have thus come to dififer. Or
to state the case in another manner : — the points in which all the
species of a genus resemble each other, and in which they differ
from allied genera, are called generic characters ; and these characters
may be attributed to inheritance from a common progenitor, for it
can rarely have happened that natural selection will have modified
Hcveral distinct species, fitted to more or less widely-different habits,
in exactly the same manner : and as these so-called generic charac-
ters have been inherited from before the period when the several
species first branched off from their common progenitor, and subse-
quently have not varied or come to difier in any degree, or only in a
slight degree, it is not probable that they should vary at the present
day. On the other hand, the points in which species differ from
other species of the same genus are called specific characters ; and as
these specific characters have varied and come to differ since the
period when the species branched off from a common progenitor, it
is probable that they should still often be in some degree variable, —
at least more variable than those parts of the organisation which
have for a very long period remained constant.

Secondary Sexual Characters Variable. — I think it will be ad-
mitted by naturalists, without my entering on details, that
secondary sexual characters are highly variable. It will also be
admitted that species of the same group differ from each other more
widely in their secondary sexual characters, than in other parts of
their organisation : compare, for instance, the amount of difference
between the males of gallinaceous birds, in which secondary sexual
characters are strongly displayed, with the amount of difference
between the females. The cause of the original variability of these
characters is not manifest ; but we can see why they should not
have been rendered as constant and uniform as others, for they are
accumulated by sexual selection, which is less rigid in its action
than ordinary selection, as it does not entail death, but only gives
fewer offspring to the less favoured males. Whatever the cause may
be of the variability of secondary sexual characters, as they are
highly variable, sexual selection will have had a wide scope for
action, and may thus have succeeded in giving to the species of the
same group a greater amount of difference in these than in other
respects.

It is a remarkable fact, that the secondary differences between
the two sexes of the same species are generally displayed in the very
same parts of the organisation in which the species of the same
genus differ from each other. Of this fact I will givo m iUus-

124 SECONDARY SEXUAL [Chap. V.

tration the two first instances which happen to stand on my list ;
and as the differences in these cases are of a very unusual nature, the
relation can hardly be accidental. The same number of joints in
the tarsi is a character common to very large groups of beetles, but
in the Engidae, as Westwood has remarked, the number varies
greatly ; and the number likewise differs in the two sexes of the
same species. Again in the fossorial hymenoptera, the neuration oi
the wings is a character of the highest importance, because common
to large groups ; but in certain genera the nem'ation differs in the
different species, and likewise in the two sexes of the same species.
Sir J. Lubbock has recently remarked, that several minute crusta-
ceans ofier excellent illustrations of this law. *'In Pontella, for
instance, the sexual characters are afforded mainly by the anterior
antennse and by the fifth pair of legs : the specific differences also
are principally given by these organs." This relation has a clear
meaning on my view : I look at all the species of the same genus as
having as certainly descended from a common progenitor, as have
the two sexes of any one species. Consequently, whatever part of
the structure of the common progenitor, or of its early descendants,
became variable, variations of this part would, it is highly probable,
be taken advantage of by natural and sexual selection, in order to fit
the several species to their several places in the economy of nature,
and likewise to fit the two sexes of the same species to each other,
or to fit the males to struggle with other males for the possession of
the females.

Finally, then, I conclude that the greater variability of specific
characters, or those which distinguish species from species, than of
generic characters, or those which are possessed by all the species ;
— that the frequent extreme variability of any part which is deve-
loped in a species in an extraordinary manner in comparison with
the same part in its congeners ; and the slight degree of variability
in a part, however extraordinarily it may be developed, if it be
common to a whole group of species ; — that the great variability of
secondary sexual characters, and their great difference in closely
allied species ; — that secondary sexual and ordinary specific differ-
ences are generally displayed in the same parts of the organisation,
— are all principles closely connected together. All being mainly
due to the species of the same group being the descendants of
a common progenitor, from whom they have inherited much in
common, — to parts which have recently and largely varied being
more hkely still to go on varying than parts which have long been
inherited and have not varied — to natural selection having more or

Chap. V.] CHARACTERS VARIABLE. 1 25

less completely, according to the lapse of time, overniastercd the
tendency to reversion and to fm'ther variability, — to sexual selection
being less rigid than ordinary selection, — and to variations in the
same parts having been accumulated by natural and sexual selection,
and having been thus adapted for secondary sexual, and for ordinary
purposes.

Distinct Species present analogous Variations, so that a Variety
of one Species often assumes a Character proper to an allied
Species, or reverts to some of the Characters of an early Progenitor.
— These propositions will be most readily understood by looking to
our domestic races. The most distinct breeds of the pigeon, in
countries widely apart, present sub-varieties with reversed feathers
on the head, and with feathers on the feet, — characters not possessed
by the aboriginal rock-pigeon ; these then are analogous variations
in two or more distinct races. The frequent presence of fourteen
or even sixteen tail-feathers in the pouter may be considered as a
variation representing the normal structure of another race, the
fantail. I presume that no one will doubt that all such analogous
variations are due to the several races of the pigeon having inherited
from a common parent the same constitution and tendency to
variation, when acted on by similar unknown influences. In the
vegetable kingdom we have a case of analogous variation, in the
enlarged stems, or as commonly called roots, of the Swedish turnip
and Kuta baga, plants which several botanists rank as varieties
produced by cultivation from a common parent : if this be not so,
the case will then be one of analogous variation in two so-called
distinct species ; and to these a third may be added, namely, the
common turnip. According to the ordinary view of each species
Having been independently created, we should have to attribute
this similarity in the enlarged stems of these three plants, not to
the vera causa of community of descent, and a consequent tendency
to vary in a like manner, but to three separate yet closely related
acts of creation. Many similar cases of analogous variation have
been observed by Naudin in the great gourd-family, and by various
authors in our cereals. Similar cases occurring with insects under
natural conditions have lately been discussed with much abihty by
Mr. Walsh, who has grouped them under his law of Equable
'Variability.

With pigeons, however, we have another case, namely, the occa-
sional appearance in all the breeds, of slaty-blue birds with two
black bars on the wings, white loins, a bar at the end of the tail,
with the outer feathers externally edged near theii* bases with
white. As all these marks are characteristic of the parent rock*

126 DISTINCT SPECIES PRESENT [Chap. V,

pigeon, I presume that no cne will doubt that this is a case of
reversion, and not of a new yet analogous variation appearing in
the several breeds. We may, I think, confidently come to this
conclusion, because, as we have seen, these coloured marks are
eminently liable to appear in the crossed offspring of two distinct
and differently coloured breeds ; and in this case there is nothing
in the external conditions of life to cause the reappearance of the
slaty-blue, with the several marks, beyond the influence of the mere
act of crossing on the laws of inheritance.

No doubt it is a very surprising fact that characters should re-
appear after having been lost for many, probably for hundreds of
generations. But when a breed has been crossed only once by some
other breed, the offspring occasionally show for many generations vi
tendency to revert in character to the foreign breed — some say, for
a dozen or even a score of generations. After twelve generations,
the proportion of blood, to use a common expression, from one
ancestor, is only 1 in 2048 ; and yet, as we see, it is generally
believed that a tendency to reversion is retained by this remnant of
foreign blood. In a breed which has not been crossed, but in which
loth parents have lost some character which their progenitor pos-
sessed, the tendency, whether strong or weak, to reproduce the lost
character might, as was formerly remarked, for all that we can see
to the contrary, be transmitted for almost any number of gener-
ations. When a character which has been lost in a breed, reappears
after a great number of generations, the most probable hypothesis
is, not that one individual suddenly takes after an ancestor
removed by some hundred generations, but that in each successive
generation the character in question has been lying latent, and at
last, under unknown favourable conditions, is developed. With the
barb-pigeon, for instance, which very rarely produces a blue bird, it
is probable that there is a latent tendency in each generation tc
produce blue plumage. The abstract improbability of such a ten-
dency being transmitted through a vast number of generations, is
not greater than that of quite useless or rudimentary organs being
similarly transmitted. A mere tendency to produce a rudiment is
indeed sometimes thus inherited.

As all the species of the same genus are supposed to be descended
from a common progenitor, it might be expected that they would
occasionally vary in an analogous manner ; so that the varieties of
two or more species would resemble each other, or that a variety
of one species would resemble ii: certain characters another and
distinct species, — this other species being, according to our view,
only a well-marked and permanent variety. But characters exclu-

ckap. v.] analogous variations. 127

sively due to analogous variation would probably be of an unim-
portant nature, for the preservation of all functionally important
characters will have been determined through natural selection, in
accordance with the different habits of the species. It might
further be expected that the species of the same genus would occa-
sionally exhibit reversions to long lost characters. As, however,
we do not know the common ancestor of any natural group, we
cannot distinguish between reversionary and analogous characters.
If, for instance, we did not know that the parent rock-pigeon was
not feather-footed or turn-crowned, we could not have told, whether
such characters in our domestic breeds were reversions or only
analogous variations ; but we might have inferred that the blue
colour was a case of reversion from the number of the markings,
which are correlated with this tint, and which would not probably
have all appeared together from simple variation. More especially
we might have inferred this, from the blue colour and the several
marks so often appearing when differently coloured breeds are
crossed. Hence, although under nature it must generally be left
doubtful, what cases are reversions to formerly existing characters,
and what are new but analogous variations, yet we ought, on our
theory, sometimes to find the varying offspring of a species assuming
characters which are already present in other members of the same
group. And this undoubtedly is the case.

The difficulty in distinguishing variable species is largely due to
the varieties mocking, as it were, other species of the same genus.
A considerable catalogue, also, could be given of forms intermediate
between two other forms, which themselves can only doubtfully bo
ranked as species ; and this shows, unless all these closely allied
forms be considered as independently created species, that they
have in varying assumed some of the characters of the others. But
the best evidence of analogous variations is afforded by parts or
organs which are generally constant in character, but which occa-
sionally vary so as to resemble, in some degree, the same part or
organ in an allied species. I have collected a long list of such
cases ; but here, as before, I lie under the great disadvantage of not
being able to give them. I can only repeat that such cases cer-
tainly occur, and seem to me very remarkable.

I will, however, give one curious and complex case, not indeed as
affecting any important character, but from occurring in several
species of the same genus, partly under domestication and partly
under nature. It is a case almost certainly of reversion. The ass
sometimes has very distinct transverse bars on its legs, like those
on the legs of the zebra : it has been asserted that these are pis inest

128 DISTINCT SPECIES PRESENT [Chap. V,

in the foal, and, from inquiries which I have made, I beUeve this
to be true. The stripe on the shoulder is sometimes double, and
is "very variable in length and outline. A white ass, but not an
albino, has been described without either spinal or shoulder stripe :
and these stripes are sometimes very obscure, or actually quite lost,
in dark-coloured asses. The koulan of Pallas is said to have been
seen with a double shoulder-stripe. Mr. Blyth has seen a specimen
of the hemionus with a distinct shoulder-stripe, though it properly
has none ; and I have been informed by Colonel Poole that the
foals of this species are generally striped on the legs, and faintly on
the shoulder. The quagga, though so plainly barred like a zebra
over the body, is without bars on the legs ; but Dr. Gray has figured
one specimen with very distinct zebra-like bars on the hocks.

With respect to the horse, I have collected cases in England of
the spinal stripe in horses of the most distinct breeds, and of all
colours : transverse bars on the legs are not rare in duns, mouse-
duns, and in one instance in a chestnut : a faint shoulder-stripe may
sometimes be seen in duns, and I have seen a trace in a bay horse.
My son made a careful examination and sketch for me of a dun
Belgian cart-horse with a double stripe on each shoulder and witK
leg-stripes ; I have myself seen a dun Devonshire pony, and a
small dun Welsh pony has been carefully described to me, both
with three parallel stripes on each shoulder.

In the north-west part of India the Kattywar breed of horses is
so generally striped, that, as I hear from Colonel Poole, who exa-
mined this breed for the Indian Government, a horse without stripes
is not considered as purely-bred. The spine is always striped ; the
legs are generally barred ; and the shoulder-stripe, which is some-
times double and sometimes treble, is common; the side of the
face, moreover, is sometimes striped. The stripes are often plainest
•in the foal ; and sometimes quite disappear in old horses. Colonel
Poole has seen both gray and bay Kattywar horses striped when
first foaled. I have also reason to suspect, from information given
me by Mr. W. W. Edwards, that with the English race-horse the
spinal stripe is much commoner in the foal than in the full-grown
animal. I have myself recently bred a foal from a bay mare (off-
spring of a Turcoman horse and a Flemish mare) by a bay English
race-horse ; this foal when a week old was marked on its hinder
quarters and on its forehead with -numerous, very narrow, dark,
zebra-like bars, and its legs were feebly striped : all the stripes soon
disappeared completely. Without here entering on further details,
I may state that I have collected cases of leg and shoulder stripes-
in horses of very different breeds in various countries from Britaia tc

'sjHAP. v.] ANALOGOUS VARIATIONS. 129

Eastern China ; and from Norway in the north to the Malay Archi-
pelago in the south. In all parts of the world these stripes occur
far oftenest in duns and mouse-duns ; by the term dun a large range
of colour is included, from one between brown and black to a close
approach to cream-colour.

I am aware that Colonel Hamilton Smith, who has written on
this subject, believes that the several breeds of the horse are
descended from several aboriginal species — one of which, the dun,
was striped ; and that the above-described appearances are all due
to ancient crosses with the dun stock. But this view may be safely
rejected ; for it is highly improbable that the heavy Belgian cart-
horse, Welsh ponies, Norwegian cobs, the lanky Kattywar race, &c.,
inhabiting the most distant parts of the world, should all have
been crossed with one supposed aboriginal stock.

Now let us turn to the effects of crossing the several species of
the horse-genus. Eollin asserts, that the common mule from the
ass and horse is particularly apt to have bars on its legs ; accord-
ing to Mr. Gosse, in certain parts of the United States about nine
out of ten mules have striped legs. I once saw a mule with its
legs so much striped that any one might have thought that it was
a hybrid-zebra ; and Mr. W. C. Martin, in his excellent treatise on
the horse, has given a figure of a similar mule. In four coloured
drawings, which I have seen, of hybrids between the ass and zebra,
the legs were much more plainly barred than the rest of the body ;
and in one of them there was a double shoulder-stripe. In Lord
Morton's famous hybrid from a chestnut mare and male quagga,
the hybrid, and even the pure offspring subsequently produced
from the same mare by a black Arabian sire, were much more
plainly barred across the legs than is even the pure quagga.
Lastly, and this is another most remarkable case, a hybrid has been
figured by Dr. Gray (and he informs me that he knows of a second
case) from the ass and the hemionus ; and this hybrid, though the
ass only occasionally has stripes on his legs and the hemionus has
none and has not even a shoulder-stripe, nevertheless had all four
legs barred, and had three short shoulder-stripes, like those on the
dun Devonshire and Welsh ponies, and even had some zebra-like
stripes on the sides of its face. With respect to this last fact, I was
so convinced that not even a stripe of colour ajipears from what is
commonly called chance, that I was led solely from the occurrence
of the face-stripes on this hybrid from the ass and hemionus to ask
Colonel Poole whether such face-stripes ever occurred in the emi-
nently striped Kattywar breed of horses, and was, as we have seen,
answered in the affirmative.

K

130 DISTIXCT SPECIES PRESENT [Chap. V,

\Vnai uow are we to say to these several facts ? We see several
distinct species of the horse-genus becoming, by simple variation,
striped on the legs like a zebra, or striped on the shoulders like an
ass. In the horse we se<3 this tendency strong whenever a dun tint
appears — a tint which approaches to that of the general colouring
of the other speoics of the genus. The appearance of the stripes is not
accompanied oy any change of form or by any other new character.
We see this tendency to become striped most strongly displayed in
hybrids from between several of the most distinct species. Now
observe the case of the several breeds of pigeons : they are descended
from a pigeon (including two or three sub-species or geographical
races) of a bluish colour, with certain bars and other marks ; and when
any breed assumes by simple variation a bluish tint, these bars and
other marks invariably reappear ; but without any other change of
form or character. When the oldest and truest breeds of various
colours are crossed, we see a strong tendency for the blue tint and bare
and marks to reappear in the mongrels. I have stated that the most
probable hypothesis to account for the reappearance of very ancient
characters, is — that there is a tendency in the young of each succes-
sive generation to produce the long-lost character, and that this
tendency, from imknown causes, sometimes prevails. And we have
just seen that in several species of the horse-genus the stripes are
either plainer or appear more commonly in the young than in the
old. Call the breeds of pigeons, some of which have bred true for
centuries, species ; and how exactly parallel is the case with that ot
the species of the horse-genus ! For myself, I venture confidently
to look back thousands on thousands of generations, and I see an
animal striped like a zebra, but perhaps otherwise very differently
constructed, the common parent of our domestic horse (whether or
not it be descended from one or more wild stocks) of the ass, the
hemionus, quagga, and zebra.

He who believes that each equine species was independently
created, will, I presume, assert that each species has been created
with a tendency to vary, both under nature and under domestication,
in this particular manner, so as often to become striped like the
other species of the genus ; and that each has been created with
a strong tendency, when cros.3ed with species inhabiting distant
quarters of the world, to produce hybrids resembling in their
stripes, not their own parents, but other species of the genus. To
admit this view is, as it seems to me, to reject a real for an unreal,
or at least for an unknown, cause. It makes the works of God a
mere mockery and deception ; I would almost as soon believe with
the old and ignorant cosmogonists, that fossil shells had never lived,

CiiAr. v.] ANALOGOUS VAIvIATIONS. 131

but had been created in stone so as to mock the shells living on the
sea-shore.

Summary. — Our ignorance of the laws of variation is profound.
Not in one case out of a hundred can we pretend to assign any
reason why this or that part has varied. But whenever we have
the means of instituting a comparision, the same laws appear to
have acted in producing the lesser differences between varieties of
the same species, and the greater differences between species of the
same genus. Changed conditions generally induce mere fluctuating
variability, but sometimes they cause direct and definite effects ;
and these may become strongly marked in the course of tim?,
though we have not sufficient evidence on this head. Habit in
producing constitutional peculiarities and use in strengthening and
disuse in weakening and diminishing organs, appear in many cases
to have been potent in their effects. Homologous parts tend to vary
in the same manner, and homologous parts tend to cohere. Modifi-
cations in hard parts and in external parts sometimes affect softer
and internal parts. When one part is largely developed, perhaps it
tends to draw nourishment from the adjoining parts ; and every
part of the structure which can be saved without detriment will be
saved. Changes of structure at an early age may affect parts sub-
sequently developed ; and many cases of correlated variation, the
nature of which we are unable to understand, undoubtedly occur.
Multiple parts are variable in number and in structure, perhaps
arising from such parts not having been closely specialised for any
particular function, so that their modifications have not been closely
checked by natural selection. It follows probably from this same
cause, that organic beings low in the scale are more variable than
those standing higher in the scale, and which have their whole
organisation more specialised. Rudimentary organs, from being
useless, are not regulated by natural selection, and hence are
variable. Specific characters — that is, the characters which have
come to differ since the several species of the same genus branched
off from a common parent — are more variable than generic cha-
racters, or those which have long been inherited, and have not
differed within this same period. In these remarks we have re-
ferred to special parts or organs being still variable, because they
have recently varied and thus come to differ ; but we have also seen
in the second chapter that the same principle applies to the whole
Individual ; for in a district where many species of a genus are
found — that is, where there has been much former variation and
differentiation, or where the manufactory of new specific forms has
been actively at work — in that district and amongst these sj^ecies,

K 2

132 LAWS OF VARIATION. [Chap. V

we now find, on an average, most varieties. Secondary sexua]
characters arc highly variable, and such characters difier much in
the species of the same group. Variability in the same parts of the
organisation has generally been taken advantage of in giving secon-
dary sexual diiferences to the two sexes of the same species, and
specific differences to the several species of the same genus. Any
part or organ developed to an extraordinary size or in an extra-
ordinary manner, in comparison with the same part or organ in the
allied species, must have gone through an extraordinary amount of
modification since the genus arose; and thus we can understand
why it should often still be variable in a much higher degree than
other parts ; for variation is a long-continued and slow process, and
natural selection will in such cases not as yet have had time to
overcome the tendency to further variability and to reversion to a
less modified state. But when a species with any extraordinarily-
developed organ has become the parent of many modified descen-
dants— which on our view must be a very slow process, requiring a
long lapse of time — in this case, natural selection has succeeded in
giving a fi.xed character to the organ, in however extraordinary a
manner it may have been developed. Species inheriting nearly the
same constitution from a common parent, and exposed to similar
influences, naturally tend to present analogous variations, or these
same species may occasionally revert to some of the characters of
their ancient progenitors. Although new and important modifica-
tions may not arise from reversion and analogous variation, such
modifications will add to the beautiful and harmonious diversity of
nature.

Whatever the cause may be of each slight difference between the
offspring and their parents — and a cause for each must exist — ^we
have reason to believe that it is the steady accumulation of bene-
ficial diflferences which has given rise to all the more important
modifications of structure in relation to tbe habits of er-ch Rpfxiiea.

Chap. Vi.] DIFFICULTIES OF THE THEORY. 133

CHAPTER YI.

Difficulties of the Theory .

Difficulties of the theory of descent with modification — Absence or rarity
of transitional varieties — Transitions in habits of life — Diversified
habits in the same species — Species with habits widely different
from these of their allies — Organs of extreme perfection — Modes of
transition — Cases of difficulty — Natura non focit saltum — Organs
of small importance — Organs not in all cases absolutely perfect —
The law of Unity of Type and of the Conditions of Existence embraced
by the theory of Natural Selection.

Long before the reader has arrived at this part of my work, a crowd
of difficulties will have occurred to him. Some of them are so
serious that to this day I can hardly reflect on them without being
in some degree staggered ; but, to the best of my judgment, the
greater number are only apparent, and those that are real are not,
1 think, fatal to the theory.

These difficulties and objections may be classed under the follow-
ing heads : — First, why, if species have descended from other species
by fine gradations, do we not everywhere see innumerable tran-
sitional forms ? Why is not all nature in confusion, instead of the
species being, as we see them, well defined ?

Secondly, is it possible that an animal having, for instance, the
structure and habits of a bat, could have been formed by the modifi-
cation of some other animal with widely-different habits and
structure? Can we believe that natural selection could produce
on the one hand, an organ of tiifling importance, such as the tail of
a giraffe, which serves as a fly-flapper, and, on the other hand, ac
organ so wonderful as the eye ?

Thirdly, can instincts be acquired and modified through natural
I Belection ? What shall we say to the instinct which leads the bee /
to make cells, and which has practically anticipated the discoveries /
of profound mathematicians ?

Fourthly, how can we account for species, when crossed, being
sterile and producing sterile offspring, whereas, when varieties are
srossed, their fertility is unimpaired ?

The two first heads will here be discussed ; some uiiscellaneou3

131 ABSENCE OR RARITY [Chap. VI.

objections in the following chapter ; Instinct and Hybridisni in the
two succeeding chapters.

On the Absence or Rarity of Transitional Varieties. — As natural
selection acts solely by the preservation of profitable modifications,
each new form will tend in a fully-stocked country to take the place
of, and finally to exterminate, its own less improved parent-form
and other less-favoured forms with which it comes into competition.
Thus extinction and natural selection go hand in hand. Hence, if
we look at each species as descended from some unknown form,
both the parent and all the transitional varieties will generally have
been exterminated by the very process of the formation and }M3r-
fection of the new form.

But, as by this theory innumerable transitional forms must have
existed, why do we not find them embedded in countless numbers
in the crust of the earth ? It will be more convenient to discuss
this question in the chapter on the Imperfection of the Geological
Kecord ; and I will here only state that I believe the answer mainly
lies in the record being incomparably less perfect than is generally
supposed. The crust of the earth is a vast museum ; but the
natural collections have been imperfectly made, and only at long
intervals of time.

But it may be urged that when several closely-allied species
inhabit the same territory, we surely oaght to find at the present
time many transitional forms. Let us take a simple case : in
i ravelling from north to south over a continent, we generally meet
at successive intervale with closely allied or representative species,
evidently filling nearly the same place in the natural economy of
the land. These representative species often meet and interlock ;
and as the one becomes rarer and rarer, the other becomes more and
more frequent, till the one replaces the other. But if we compare
these species where they intermingle, they are generally as absolutely
distinct from each other in every detail of structure as are specimens
taken from the metropolis inhabited by each. By my theory these
allied species are descended from a common parent ; and during the
process of modification, each has become adapted to the conditions
of life of its own region, and has supplanted and exterminated its
original parent-form and all the transitional varieties between its
past and present states. Hence we ought not to expect at the
present time to meet with numerous transitional varieties in each
region, though they must have existed there, and may be embedded
there in a fossil condition. But in the intermediate region, having
intermediate conditions of life, why do we not now find closely-
linking intermediate varieties? This difllculty for a long time

Chap. VL] OF IFANSITIONAL VARIETIES. 135

quite confounded me. But I think it can be in large part ex-
plained.

In the first place we should be extremely cautious in inferring,
because an area is now continuous, that it has been continuous
during a long period. Geology would lead us to believe that most
continents have been broken up into islands even during the later
tertiary periods ; and in such islands distinct species might have
been separately formed without the possibility of inteniicdiate
varieties existing in the intermediate zones. By changes in the
form of the land and of climate, marine areas now continuous must
often have existed within recent times in a far less continuous and
uniform condition than at present. But I will pass over this way
of escaping from the difficulty ; for I believe that many perfectly
defined species have been formed on strictly continuous areas ;
though I do not doubt that the formerly broken condition of areas
now continuous, has played an important part in the formation of new
species, more especially with freely-crossing and wandering animals.

in looking at species as they are now distributed over a wide
area, we generally find them tolerably numerous over a large
territory, then becoming somewhat abruptly rarer and rarer on the
confines, and finally disappearing. Hence the neutral territory
between two representative species is generally narrow in comparison
with the territory proper to each. We see the same fact in
ascending mountains, and sometimes it is quite remarkable how
abruptly, as Alph. de Candolle has observed, a common alpine
species disappears. The same fact has been noticed by E. Forbes
in sounding the depths of the sea with the dredge. To those who
look at climate and the physical conditions of life as the all-
important elements of distribution, these facts ought to cause
surprise, as climate and height or depth graduate away insensibly.
But when we bear in mind that almost every species, even in its
metropolis, would increase immensely in numbers, were it not for
other competing species ; that nearly all either prey on or serve as
prey for others ; in short, that eacn organic being is either directly
or indirectly related in the most important manner to other organic
beings, — we see that the range of the inhabitants of any country
by no means exclusively depends on insensibly changing physical
conditions, but in a large part on the presence of other species, on
which it lives, or by which it is destroyed, or with which it comes
into competition ; and as these species are already defined objects,
not blending one into another by insensible gradations, the range of
any one species, depending as it does on the range of others, will
tend to be sharply defined. Moreover, each species on the confines

130 ABSENCE OR RARITY [Chap.\1.

of its range, where it exists in lessened numbers, will, during fluctu-
ations in the number of its enemies or of its prey, or in the nature
of the seasons, be extremely liable to utter extermination ; and thus
its geographical range will come to be still more sharply defined.

As allied or representative species, when inhabiting a continuous
area, are generally distributed in such a manner that each has a
wide range, with a comparatively narrow neutral territory between
them, in which they become rather suddenly rarer and rarer ; then,
as varieties do not essentially differ from species, the same rule will
probably apply to both ; and if we take a varying species inhabiting
a very large area, we shall have to adapt two varieties to two large
areas, and a third variety to a narrow intermediate zone. The
intermediate variety, consequently, will exist in lesser numbers
from inhabiting a narrow and lesser area ; and practically, as far as
I can make out, this rule holds good with varieties in a state of
nature. I have met with striking instances of the rule in the case
of varieties intermediate between well-marked varieties in the genus
Balanus. And it would appear from information given me by Mr.
Watson, Dr. Asa Gray, and Mr. Wollaston, that generally, when
varieties intermediate between two other forms occur, they are much
rarer numerically than the forms which they connect. Now, if we
may trust these facts and inferences, and conclude that varieties
linking two other varieties together generally have existed in lesser
numbers than the forms which they connect, then we can understand
why intermediate varieties should not endure for very long periods :
— why, as a general rule, they should be exterminated and disappear,
fiooner than the forms which they originally linked together.

For any form existing in ksser numbers would, as already
remarked, run a greater chance of being exterminated than one
existing in large numbers ; and in this particular case the inter-
mediate form would be eminently liable to the inroads of closely-
allied forms existing on both sides of it. But it is a far more
important consideration, that during the process of further modifi-
cation, by which two varieties are supposed to be converted and
perfected into two distinct species, the two which exist in larger
numbers, from inhabiting larger areas, will have a great advantage
over the intermediate variety, which exists in smaller numbers
in a narrow and intermediate zone. For forms existing in larger
numbers will have a better chance, within any given period, of
presenting further favourable variations for natural selection to
seize on, than will the rarer forms which exist in lesser numbers.
ITence, the moT3 common forms, in the race for life, will tend to
beat and supplant the less common forms, for these wuU be mora

Chap. VI.] OF TRANSITIONAL VARIETIES 137

slowly modified and improved. It is the same principle which, as
I believe, accounts for the common species in each coimtry, as
shown in the second chapter, presenting on an average a greater
number of well-marked varieties than do the rarer species. I may
illustrate what I mean by supposing three varieties of sheep to be
kept, one adapted to an extensive mountainous region ; a second
to a comparatively narrow, hilly tract; and a third to the wide
plains at the base ; and that the inhabitants are all trying with
equal steadiness and skill to improve their stocks by selection ; the
chances in this case will be strongly in favour of the great holders
on the mountains or on the plains, improving their breeds more
quickly than the small holders on the intermediate narrow, hilly
tract ; and consequently the improved mountain or plain breed will
soon take the place of the less improved hill breed ; and thus the
two breeds, which originally existed in greater numbers, will come
into close contact with each other, without the interposition of the
supplanted, intermediate hill- variety.

To sum up, I believe that species come to be tolerably well-
defined objects, and do not at any one period present an inextricable
chaos of varying and intermediate links : first, because new varie-
ties are very slowly formed, for variation is a slow process, and
natural selection can do nothing until favourable individual
differences or variations occur, and until a place in the natural
polity of the country can be better filled by some modification of
some one or more of its inhabitants. And such new places will
depend on slow changes of climate, or on the occasional immigration
of new inhabitants, and, probably, in a still more important degree,
on some of the old inhabitants becoming slowly modified, with the
new forms thus produced and the old ones acting and reacting on
each other. So that, in any one region and at any one time, we
ought to see only a few species presenting slight modifications of
structure in some degree permanent ; and this assuredly we do see.

Secondly, areas now continuous must often have existed within
the recent period as isolated portions, in which many forms, more
especially amongst the classes which unite for each birth and
wander much, may have separately been rendered sufficiently
distinct to rank as representative species. In this case, inter-
mediate varieties between the several representative species and
their common parent, must formerly have existed within each
isolated portion of the land, but these links during the process of
natural selection will have been supplanted and exterminated, so
that they will no longer be found in a living state.

Thirdly, when two or more varieties have been formed in different

138 TRANSITIONS OF ORGANIC BEINGS. [C^'hap. VL

portions of a strictly continuous area, intermediate varieties will, it
is probable, at first have been formed in the intermediate zones, but
they will generally have had a short duration. For these inter-
mediate varieties will, frcm reasons already assigned (namely from
what we know of the actual distribution of closely allied or repre-
sentative species, and likewise of acknowledged varieties), exist in
the intermediate zones in lesser numbers than the varieties which
they tend to connect. From this cause alone the intermediate
varieties will bo liable to accidental extermination ; and during the
process of further modification through natural selection, they will
almost certainly be beaten and supplanted by the forms which they
connect ; for these from existing in greater numbers will, in the
aggregate, present more varieties, and thus be further improved
through natural selection and gain further advantages.

Lastly, looking not to any one time, but to all time, if my theory
be true, numberless intermediate varieties, linking closely together
all the species of the same group, must assuredly have existed ; but
the very process of natural selection constantly tends, as has been.
60 often remarked, to exterminate the parent-forms and the inter-
mediate links. Consequently evidence of their former existence
could be found only amongst fossil remains, which are preserved, as
we shall attempt to show in a future chapter, in an extremely im-
perfect and intermittent record.

071 the Origin and Transitions of Organic Beings with ^peculiar
Ilahits and Structure. — It has been asked by the opponents of such
views as I hold, how, for instance, could a land carnivorous animal
have been converted into one with aquatic habits ; for how could
the animal in its transitional state have subsisted ? It would be
easy to show that there now exist carnivorous animals presenting
close intermediate grades from strictly terrestrial to aquatic habits :
and as each exists by a struggle for life, it is clear that each must be
well adapted to its place in nature. Look at the Mustela vison of
North America, which has webbed feet, and which resembles an
otter in its fur, short legs, and form of tail. During the summer
this animal dives for and preys on fish, but during the long winter
it leaves the frozen waters, and preys, like other pole-cats, on mice
and land animals. If a different case had been taken, and it had
been asked how an insectivorous quadruped could possibly have been
converted into a flying bat, the question would have been far more
difficult to answer. Yet I think such difficulties have little weight.

Here, as on other occasions, I lie under a heavy disadvantage, for,
out of the many striking case? which I have collected, I can give
only one or two instances of transitional habits and st<-ucturc8 in

CilAP. VI.] TRANSITIONS OF ORGANIC BEINGS. 139

allied species ; and of diversified habits, eitlier constant or occa-
Bional, in the same species. And it seems to me that nothing less
than a long list of such cases is sufficient to lessen the difficulty in
any particular case like that of the bat.

Look at the family of squirrels ; here we have the finest gra
dation from animals with their tails only slightly flattened, and
from others, as Sir J. Richardson has remarked, with the posterior
part of their bodies rather wide and with the skin on their flanks
rather full, to the so-called flying squirrels ; and flying squirrels
have their limbs and even the base of the tail united by a broad
expanse^ skin, which serves as ajQarachute and allows tliem to
glide through the air to an astonishing distance from tree to tree.
We cannot doubt that each structure is of use to each kind of
squirrel in its own country, by enabling it to escape birds or beasts
of prey, to collect food more quickly, or, as there is reason to
believe, to lessen the danger from occasional falls. But it does not
follow from this fact that the structure of each squirrel is the best
that it is possible to conceive under all possible conditions. Let
the climate and vegetation change, let other competing rodents or
new beasts of prey immigrate, or old ones become modified, and all
analogy would lead us to believe that some at least of the squirrels
would decrease in numbers or become exterminated, unless they
also became modified and improved in structure in a corresponding
manner. Therefore, I can see no difficulty, more especially under
changing conditions of life, in the continued preservation of indi-
viduals with fuller and fuller flank-membranes, each modification
being useful, each being propagated, until, by the accumulated
effects of this process of natural selection, a perfect so-called flying
squirrel was produced.

Now look at the Galeopithecus or so-called flying lemur, which
formerly was ranked amongst bats, but is now believed to belong
to the Insectivora. An extremely wide flank-membrane stretches
from the corners of the jaw to the tail, and includes the limbs
with the elongated fingers. This flank-membrane is furnished with
an extensor muscle. Although no graduated links of structure, fitted
for gliding through the air, now connect the Galeopithecus with
the other Insectivora, yet there is no difficulty in supposing that
such links formerly existed, and that each was developed in the
same manner as with the less perfectly gliding squirrels ; each grade
of structure having been useful to its possessor. Nor can I sue
any insuperable diffictilty in further believing that the membrune
connected fingers and fore-arm of the Galeopithecus might have
been greatly lengthened by natural selection ; and this, as far as t!i«

140 TRANSITIONS OF ORGANIC BEINGS [Chap. VL

organs of flight are concerned, ssrould have converted the animal
into a bat. In certain bats in which the wing-membrane extends
from the top of the shoulder to the tail and includes the hind-legs,
we perhaps see traces of an apparatus originally fitted for gliding
through the air rather than for flight.

If about a dozen genera of birds were to become extinct, who
would have ventured to surmise that birds might have existed
which used their wings solely as flappers, like the logger-headed
duck (Micropterus of Eyton) ; as fins in the water and as front-legs
on the land, like the penguin ; as sails, Uke the ostrich ; and func-
tionally for no purpose, like the Apteryx ? Yet the structure of
each of these birds is good for it, under the conditions of life to
which it is exposed, for each has to live by a struggle ; but it is not
necesarily the best possible under all possible conditions. It must
not be inferred from these remarks that any of the grades of wing-
structure here alluded to, which perhaps may all be the result of
disuse, indicate the steps by which birds actually acquired their
perfect power of flight; but they serve to show what diversified
means of transition are at least possible.

Seeing that a few members of such v/ater-breathing classes as
the Crustacea and Mollusca are adapted to live on the land ; and
seeing that we have flying birds and mammals, flying insects of the
most diversified types, and formerly had flying reptiles, it is con-
ceivable that flying-fish, which now glide far through the air,
slightly rising and turning by the aid of their fluttering fins, might
have been modified into perfectly winged animals. If this had
been effected, who would have ever imagined that in an early
transitional state they had been the inhabitants of the open ocean,
and had used their incipient organs of flight exclusively, as far as
we know, to escape being devoured by other fish ?

When we see any structure highly perfected for any particular
habit, as the wings of a bird for flight, we should bear in mind that
animals displaying early transitional grades of the structure \\i\]
seldom have survived to the present day, for they will have been
supplanted by their successors, which were gradually rendered more
perfect through natural selection. Furthermore, we may conclude
that transitional states between structures fltted for very different
habits of life will rarely have been developed at an early period in
great numbers and under many subordinate forms. Thus, to return
to our imaginary illustration of the flying-fish, it does not seem
probable that fishes capable of true flight would have been developed
under many subordinate forms, for taking prey of many kinds in
many ways, on the land and in the water, until their organs of flight

Chap. VI.] TRANSITIONS OF ORGANIC BEINGS. 141

had come to a high stage of perfection, so as to have given them a
decided advantage over other animals in the battle for life. Hence
the chance of discovering species with transitional grades of struc-
ture in a fossil condition will always be less, from their having
existed in lesser numbers, than in the case of species with fully
developed structures.

I will now give two or three instances both of diversified and of
changed habits in the individuals of the same species. In either
case it would be easy for natural selection to adapt the structure
of the animal to its changed habits, or exclusively to one of its
several habits. It is, however, difficult to decide, and immaterial
for us, whether habits generally change first and structure after-
wards ; or whether slight modifications of structure lead to clianged
habits ; both probably often occurring almost simultaneously. Of
cases of changed habits it will suffice merely to allude to that of the
many British insects which now feed on exotic plants, or exclu-
sively on artificial substances. Of diversified habits innumerable
instances could be given : I have often watched a tyrant flycatcher
(Saurophagus sulphuratus) in South America, hovering over one
spot and then proceeding to another, like a kestrel, and at other
times standing stationary on the margin of water, and then dashing
into it like a kingfisher at a fish. In our own country the larger
titmouse (Parus major) may be seen climbing branches, almost like
a creeper ; it sometimes, like a shrike, kills small birds by blows
on the head ; and I have many times seen and heard it hammering
the seeds of the yew on a branch, and thus breaking them like a
nuthatch. In North America the black bear was seen by Hearne
swimming for hours with widely open mouth, thus catching, almost
like a whale, insects in the water.

As we sometimes see individuals following habits different from
those proper to their species and to the other species of the same
genus, we might expect that such individuals would occasionally
give rise to new species, having anomalous habits, and with their
structure either slightly or considerably modified from that of
their type. And such instances occur in nature. Can a more
striking instance of adaptation be given than that of a woodpecker
for climbing trees and seizing insects in the chinks of the bark ? Yet
in North America there are woodpeckers which feed largely on fruit,
and others with elongated wings which chase insects on the wing.
On the plains of La Plata, where hardly a tree grows, there is a
woodpecker (Colaptes campestris) which has two toes before and
two behind, a long pointed tongue, pointed tail-feathers, sufficiently
stiff to support the bird in a vertical position on a post, but not so

142 TRANSITIONS OF ORGANIC BEINGS. [Chap. VI.

stiff as in the typical woodpeckers, and a straight strong beak. The
beak, however, is not so straight or so strong as in the typical
woodpeckers, but it is strong enough to bore into wood. Hence
this Colaptes in all the essential parts of its structure is a vrood-
pecker. Even in such trifling characters as the colouring, the
harsh tone of the voice, and undulatory Aight, its close blood-
relationship to our common woodpecker is plainly declared; yet,
as I can assert, not only from my own observations, but from those
of the accurate Azara, in certain large districts it does not climb
trees, and it makes its nest in holes in banks ! In certain other
districts, however, this same woodpecker, as Mr. Hudson states,
frequents trees, and bores holes in the trunk for its nest. I may
mention as another illustration of the varied habits of this genus,
that a Mexican Colaptes has been described by De Saussure as
boring holes into hard wood in order to lay up a store of acorns.

Petrels are the most aerial and oceanic of birds, but in the quiet
sounds of Tierra del Fuego, the Puffinuria berardi, in its general
habits, in its astonishing power of diving, in its manner of swim-
ming and of flying when made to take flight, would be mistaken
by any one for an auk or a grebe ; nevertheless it is essentially a
petrel, but with many parts of its organisation profoundly modified
in relation to its new habits of life ; whereas the woodpecker ot
La Plata has had its structure only slightly modified. In the case
of the water-ouzel, the acutest observer by examining its dead body
would never have suspected its sub-aquatic habits ; yet this bird,
which is allied to the thrush family, subsists by diving — using its
wings under water, and grasping stones with its feet. All the
members of the great order of llymenopterous insects are terrestrial,
excepting the genus Proctotrupes, which Sir John Lubbock has
discovered to be aquatic in its habits ; it often enters the water and
dives about by the use not of its legs but of its wings, and remains
as long as four hours beneath the surface ; yet it exhibits no modi-
fication in structure in accordance with its abnormal habits.

He who believes that each being has been created as we now see
it, must occasionally have felt surprise when he has met with an
animal having habits and structure not in agreement. What can
be plainer than that the webbed feet of ducks and geese are formed
for swimming ? Yet there are upland geese with webbed feet which
rarely go near the water ; and no one except Audubon has seen the
frigate-bird, which has all its four toes webbed, alight on the surface
of the ocean. On the other hand, grebes and coots are eminently
aquatic, although their toes are only bordered by membrane. What
seems plainer than that the long toes, not furnished with membrane

Chap. VI.] ORGANS OF EXTREME PERFECTION. 143

of the Grallatores are formed for walking over swamps and floating
plants? — the water-hen and landrail are members of this order,
yet the first is nearly as aquatic as the coot, and the second nearly
as terrestrial as the quail or partridge. In such cases, and many
others could be given, habits have changed without a corresponding
change of structure. The webbed feet of the upland goose may be
said to have become almost rudimentary in function, though not
in structure. In the frigate-bird, the deeply scooped membrane
between the toes shows that structure has begun to change.

He who believes in separate and innumerable acts of creation
may say, that in these cases it has pleased the Creator to cause a
being of one type to take the place of one belonging to another
type ; but this seems to me only re-stating the fact in dignified
language. He who believes in the struggle for existence and in the
principle of natural selection, will acknowledge that eveiy organic
being is constantly endeavouring to increase in numbers ; and that
if any one being varies ever so little, either in habits or structure,
and thus gains an advantage over some other inhabitant of the
same country, it will seize on the place of that inhabitant, however
different that may be from its own place. Hence it will cause him
no surprise that there should be geese and frigate-birds with webbed
feet, living on the dry land and rarely alighting on the water •
that there should be long-toed corncrakes, living in meadows in-
stead of in swamps ; that there should be woodpeckers where hardly
a tree grows ; that there should be diving tlirushes and diving
Hymenoptera, and petrels with the habits of auks.

Organs of extreme Perfection and Complication.

To suppose that the eye with all its inimitable contrivances for
adjusting the focus to different distances, for admitting different
amounts of light, and for the~correction of spherical and chromatic
aberration, could have been formed by natiiraT" selection, seems,
I freely confess, absurd in the highest degree. When it was first
said that the sun stood still and the world turned round, the
common sense of mankind declared the doctrine false ; but the old
saying of Vox jpopulij vox Dei, as every philosopher knows, cannot
be trusted in science. Reason tells me, that if numerous gradations
from a simple and imperfect eye to one complex and perfect can
bo shown to exist, each grade being; useful to its possessor, as is
certainly the case ; if further, the eye ever varies and the variations
be inherited, as is likewise certainly the case ; and if such varia-
tions should be useful to any animal under changing conditions of
life, then the difficulty of believing that a perfect and complex ej^

144

ORGANS OF EXTREME PERFECTION. [Ceap. VI,

^

■i

could he formed by natural selection, though insuperable by our
imaf^ination, should not be considered as subversive of the theory.
How a nerve comes to be sensitive to light, hardly concerns us
more than how life itself originated ; but I may remark that, as
some of the lowest organisms, in which nerves cannot be Getected,
are capable of perceiving light, it does not seem impossible that
certain sensitive elements in their sarcode should become aggregated
and developed into nerves, endowed wit¥ this sp.eciad,§eji§ibility.'~

In searching for the gradations through which an organ in any
species has been perfected, we ought to look exclusively to its lineal
progenitors ; but this is scarcely ever possible, and we are forced to
look to other species and genera of the same group, that is to the
collateral descendants from the same parent-form, in order to see
what gradations are possible, and for the chance of some gradations
having been transmitted in an unaltered or little altered condition.
But the state of the same organ in distinct classes may incidentally
throw light on the steps by which it has been perfected.

The simplest organ which can be called an eye consists of an
optic nerve, surrounded by pigment-cells and covered by translucent
skin, but without any lens or other refractive body. We may,
however, according to M. Jourdain, descend even a step lower
and find aggregates of pigment-cells, apparently serving as organs
of vision, without any nerves, and resting merely on sarcodic tissue.
Eyes of the above simple nature are not capable of distinct vision^
and serve only to distinguish light from darkness. In certain star-
fishes, small depressions in the layer of pigment which surrounds
the nerve are filled, as described by the author just quoted, with
transparent gelatinous matter, projecting with a convex surface, like
the cornea in the higher animals. He suggests that this serves not
to form an image, but only to concentrate the luminous rays and
render their perception more easy. In this concentration of the
rays we gain the first and by far the most important step towards
the formation of a true, picture-forming eye ; for we have only to
place the naked extremity of the optic nerve, which in some of the
lower animals lies deeply buried in the body, and in some near
the surface, at the right distance from the concentrating apparatus,
and an image will be formed on it.

In the great class of the Articulata, we may start from an optic
nerve simply coated with pigment, the latter sometimes forming a
sort of pupil, but destitute of a lens or other optical contrivance.
With insects it is now known that the numerous facets on the
cornea of their great compound eyes form true lenses, and that
the cones include curiously modified nervous filaments. But these

CiiAP. VI.J ORGANS OF EXTREME PERFECTION. 145

organs in the Aiticulata are so much diversified that MUllcr fonnerly
made three main classes with seven subdivisions, besides a fourth
main class of aggregated simple eyes.

When we reflect on these facts, here given much too briefly, with
respect to th« wide, diversified, and graduated range of structure in
the eyes of the lower animals ; and when we bear in mind how
small the number of all living forms must be in comparison with
those which have become extinct, the difficulty ceases to be very
gi-eat in believing that natural selection may have converted the
simple apparatus of an optic nerve, coated with pigment and
invested by transparent membrane, into an optical instrument as
perfect as is possessed by any member of the Articulate Class.

He who will go thus far, ought not to hesitate to go one step
fuither, if he finds on finishing this volume that large bodies
of facts, otherwise inexplicable, can be explained by the theory of
modification through natural selection ; he ought to admit that a
structure even as perfect as an eagle's eye might thus be formed,
although in this case he does not know the transitional states. It
has been objected that in order to modify the eye and still preserve
it as a perfect instrument, many changes would have to be effected
simultaneously, which, it is assumed, could not be done through
natural selection ; but as I have attempted to show in my work on
the variation of domestic animals, it is not necessary to suppose
that the modifications were all simultaneous, if they were extremely
slight and gradual. Different kinds of modification would, also,
serve for the same general purpose : as Mr. Wallace has remarked,
" if a lens has too short or too long a focus, it may be amended
either by an alteration of curvature, or an alteration of density ; if
the curvature be irregular, and the rays do not converge to a point,
then any increased regularity of curvature will be an improvement.
So the contraction of the iris and the muscular movements of the
eye are neither of them essential to vision, but only improvements
which might have been added and perfected at any stage of the
construction of the instrument." Within the highest division of
the animal kingdom, namely, the Vertebrata, we can start from an
eye so simple, that it consists, as in the lancelet, of a little sack of
transparent skin, furnished with a nerve and lined with pigment,
but destitute of any other apparatus. In fishes and reptiles, as
Owen has remarked, " the range of gradations of dioptric structures
is very great." It is a significant fact that even in man, according
to the high authority of Virchow, the beautiful crystalline lens is
formed in the embryo by an accumulation of epidermic cells, lying
in a sack-like fold of the skin ; and the vitreous body is formed

L

1-16 MODES OF TRANSITION. [CiiAP. VI

from embryonic sub-cutaneous tissue. To arrive, however, at a
just conclusion regarding the formation of the eye, with all its mar-
vellous yet not absolutely perfect characters, it is indispensable
that the reason should conquer the imagination ; but I have felt
the difficulty far too keenly to be surprised at others hesitating to
extend the principle of natural selection to so startling a length.

It is scarcely possible to avoid comparing the eye with a telescope.
"We know that this instrument has been perfected by the long-
continued efforts of the highest human intellects ; and we naturally
infer that the eye has been formed by a somewhat analogous
process. But may not this inference be presumptuous ? Have we
any right to assume that the Creator works by intellectual povrers
like those of man? If we must compare the eye to an optical
instrument, we ought in imagination to take a thick layer of
transparent tissue, with spaces filled with fluid, and with a nerve
sensitive to light beneath, and then suppose every part of this layer
to be continually changing slowly in density, so as to separate into
layers of different densities and thicknesses, placed at different
distances from each other, and with the surfaces of each la3''er
clowly changing in form. Further we must suppose that there is a
power, represented by natural selection or the survival of the fittest,
always intently watching each slight alteration in the transparent
layers ; and carefully preserving each which, under varied circum-
stances, in any way or in any degree, tends to produce a distincter
image. We must suppose each new state of the instrument to be
/nultii)lied by the million ; each to be preserved until a better one
is produced, and then the old ones to be all destroyed. In living
bodies, variation will cause the slight alterations, generation will
multiply them almost infinitely, and natural selection will pick out
with unerring skill each improvement. Let this process go on for
millions of years ; and during each year on millions of individuals
of many kinds ; and may we not believe that a living optical
instrument might thus be formed as sujjerior to one of glass, as the
works of the Creator are to those of man ?

Modes of Transition.

If it could be demonstrated that any complex organ existed,
which could not possibly have been formed by numerous, suc-
cessive, slight modifications, my theory would absolutely break
down. But I can find out no such case. No doubt many organs
exist of which we do not know the transitional grades, more espe-
cially if we look to m-uch-isolated species, round which, according to
the theory, there has been mich extinction. Or again, if we take

CuAi». VI. J MODES OF TRANSITION. 147

an organ common to all the members of a class, for in this latter
case the organ must have been originally formed at a remote period,
since which all the many members of the class have been developed;
and in order to discover the early transitional grades through which
the organ has passed, we should have to look to very ancient ances-
tral forms, long since become extinct.

We should be extremely cautious in concluding that an organ
could not have been formed by transitional gradations of some kind.
Numerous cases could be given amongst the lower animals of the
same organ performing at the same time wholly distinct functions ;
thus in the larva of the dragon-fly and in the fish Cobites the
alimentary canal respires, digests, and excretes. In the Hydra, the
animal may be turned inside out, and the exterior surface will then
digest and the stomach respire. In such cases natural selection
might specialise, if any advantage were thus gained, the whole or
part of an organ, which had previously performed two functions, for
one function alone, and thus by insensible steps greatly change its
nature. Many plants are known which regularly produce at the
same time differently constructed flowers ; and if such plants were
to produce one kind alone, a great change would be effected with
comparative suddenness in the character of the species. It is, how-
ever, probable that the two sorts of flowers borne by the same plant
were originally differentiated by finely graduated steps, which may
still be followed in some few cases.

Again, two distinct organs, or the same organ under two very
different forms, may simultaneously perform in the same individual
the same function, and this is an extremely important means of
transition : to give one instance, — there are fish with gills or
branchia3 that breathe the air dissolved in the water, at the same
time that they breathe free air in their swimbladders, this latter
organ being divided by highly vascular partitions, and having a
ductus pneumaticus for the supply of air. To give another instance
from the vegetable kingdom : plants climb by three distinct means,
by spirally twining, by clasping a support with their sensitive
tendrils, and by the emission of aerial rootlets ; these three means
are usually found in distinct groups, but some few species exhibit
two of the means, or even all three, combined in the same indivi-
dual. In all such cases one of the two organs might readily be
modified and perfected so as to perform all the work, being aided
during the progress of modification by the other organ ; and then
this other organ might be modified for some other and quite distinct
purpose, or be wholly obliterated.
^ The illustration of the swimbladder in fishes is a good one.

148 MODES OF TRANSITION. [Chap. VI.

because it shows us clearly the highly important fact that an organ
originally constructed for one purpose, namely, flotation, may be
converted into one for a widely different purpose, namely, respiration.
The swimbladder has, also, been worked in as an accessory to the
auditory organs of certain fishes. All physiologists admit that
the swimbladder is homologous, or " ideally similar " in position and
structure with the lungs of the higher vertebrate animals : hence
there is no reason to doubt that the swimbladder has actually
been converted into lungs, or an organ used exclusively for
respiration.

According to this view it may be inferred that all vertebrate
animals with true lungs are descended by ordinary generation from
an ancient and unknown prototype, which was furnished with a
floating apparatus or swimbladder. We can thus, as I infer from
Owen's interesting description of these parts, understand the strange
fact that every particle of food and drink which we swallow has to
pass over the orifice of the trachea, with some risk of falling into
the lungs, notwithstanding the beautiful contrivance by which the
glottis is closed. In the higher Vertebrata the branchice have
wholly disappeared — but in the embryo the slits on the sides of the
neck and the loop-like course of the arteries still mark their former
position. But it is conceivable that the now utterly lost branchire
might have been gradually worked in by natural selection for some
distinct purpose : for instance, Landois has shown that the wings
of insects are developed from the tracheee ; it is therefore highly
probable that in this great class organs which once served for
respiration have been actually converted into organs for flight.

In considering transitions of organs, it is so important to bear in
mind the probability of conversion from one function to another,
that I will give another instance. Pedunculated cirripedes have
two minute folds of skin, called by me the ovigerous frena, which
fierve, through the means of a sticky secretion, to retain the eggs
until they are hatched within the sack. These cirripedes have no
branchise, the whole surface of the body and of the sack, together
with the small frena, serving for respiration. The Balanidas or
sessile cirripedes, on the other hand, have no ovigerous frena, the
eggs lying loose at the bottom of the sack, within the well-enclosed,
^shell ; but they have, in the same relative position with the frena,
large, much-folded membranes, which freely communicate with the
circulatory lacunas of the sack and body, and which have been
considered by all naturalists to act as branchiae. Now I think no
one will dispute that the ovigerous frena in the one family are)
strictly homologous with the brancL'^e of the other family ; indeed,!

Chap. VI.] MODES OF TRANSITION. 14S

they graduate into each other. Therefore it need not be doubted
that the two little folds of skin, which originally served as
ovigerous frena, but which, likewise, very slightly aided in the
act of respiration, have been gradually converted by natural
selection into branchiae, simi)ly through an increase in their size
and the obliteration of their adhesive glands. If all pedunculated
cirripedes had become extinct, and they have suffered far more
extinction than have sessile cirripedes, who would ever have
imagined that the branchiae in this latter family had originally
existed as organs for preventing the ova from being washed out of
the sack ?

There is another possible mode of transition, namely, through
the acceleration or retardation of the period of reproduction. This
has lately been insisted on by Prof. Cope and others in the United
States. It is now known that some animals are capable of repro-
duction at a very early age, before they have acquired their perfect
characters ; and if this power became thoroughly well developed in
a species, it seems probable that the adult stage of development
would sooner or later be lost ; and in this case, especially if the
larva differed much from the mature form, the character of the
species would be greatly changed and degraded. Again, not a few
animals, after arriving at maturity, go on changing in character
during nearly their whole lives. With mammals, for instance, the
form of the skull is often much altered with age, of which Dr.
Murie has given some striking instances with seals ; every one
knows how the horns of stags become more and more branched,
and the plumes of some birds become more finely developed, as
they grow older. Prof. Cope states that the teeth of certain lizards
change much in shape with advancing years ; with crustaceans not
only many trivial, but some important parts assume a new
character, as recorded by Fritz Miiller, after maturity. In all such
cases, — and many could be given, — if the age for reproduction were
retarded, the character of the species, at least in its adult state,
would be modified; nor is it improbable that the previous and
earlier stages of development would in some cases be hurried
through and finally lost. Whether species have often or ever been
modified through this comparatively sudden mode of transition, 1
can form no opinion ; but if this has occurred, it is probable that
the differences between the young and the mature, and betweeo
the mature and the old, were primordially acquired by graduated
eteps.

150 DIFFICULTIES OF THE iHEORY [Ciijlp. VI.

SpecLil Difficulties of the Theory of Natural Selection.

Although we must be extremely cautious in concluding that any
organ could not have been produced by successive, small, tran-
sitional gradations, yet undoubtedly serious cases of difficulty occur.

One of the most serious is that of neuter insects, which are often
differently constructed from either the males or fertile females ; but
this case will be treated of in the next chapter. The electric
organs of fishes offer another case of special difficulty; for it is
impossible to conceive by what steps these wondrous organs have
been produced. But this is not surprising, for we do not even
know of what use they are. In the Gymnotus aud Torpedo they
no doubt serve as powerful means of defence, and perhaps fot
securing prey; yet in the Eay, as observed by Matteucci, an
analogous organ in the tail manifests but little electricity, even
when the animal is greatly irritated; so little, that it can
hardly be of any use for the above purposes. ]\Torcover, in the
Hay, besides the organ just referred to, there is, as Dr. R. M'Donneil
has shown, another organ near the head, not known to be electrical,
but which appears to be the real homologue of the electric battery
in the Torpedo. It is generally admitted that there exists between
these organs and ordinary muscle a close analogy, in intimate
structure, in the distribution of the nerves, and in the manner in
which they are acted on by various reagents. It should, also, be
especially observed that muscular contraction is accompanied by an
electrical discharge ; and, as Dr. Eadcliffe insists, " in the electrical
apparatus of the torpedo during rest, there would seem to be a
charge in every respect like that which is met with in muscle and
nerve during rest, and the discharge of the torpedo, instead of being
peculiar, may be only another form of the discharge which attends
upon the action of muscle and motor nerve." Beyond this we can-
not at present go in the way of explanation ; but as we know so
little about the uses of these organs, and as we know nothing about
the habits and structure of the progenitors of the existing electric
fishes, it w^ould be extremely bold to maintain that no serviceable
transitions are possible by which these organs might have been
gradually developed.

These organs appear at first to offer another and far more serious
difficulty ; for they occur in about a dozen kinds of fish, of which
several are widely remote in their affinities. When the same organ
is fouDd in several members of the same class, especially if in
mcmbeis having very different habits of life, we may generally
attribute its presence to inheritance from a common ancestor ; a:id

^i!Ar. VL] OF NATURAL SELECTION. 151

its absence in some of the members to loss through disuse or
natural selection. So that, if the electric organs had been
inherited from some one ancient progenitor, we might have
expected that all electric fishes would have been specially related
to each other ; but this is far from the case. Nor does geology at
all lead to the belief that most fishes formerly possessed electric
organs, which their modified descendants have now lost. But
when we look at the subject more closely, we find in the several
fishes provided with electric organs, that these are situated in dif-
ferent parts of the body, — that they differ in construction, as in
the arrangement of the plates, and, according to Pacini, in the
process or means by which the electricity is excited — and lastly, in
being supplied with nerves proceeding from different sources, and
this is perhaps the most important of all the differences. Hence in
the several fishes fi:./nished with electric organs, these cannot be
considered as homologous, but only as analogous in function. Con-
sequently there is no reason to suppose that they have been inherited
from a common progenitor ; for had this been the case they would
have closely resembled each other in all respects. Thus the difficulty
of an organ, apparently the same, arising in several remotely allied
species, disappears, leaving only the lesser yet still great difiSculty ;
namely, by what graduated steps these organs have been developed
in each separate group of fishes.

The luminous organs which occur in a few insects, belonging
to widely different families, and which are situated in different
parts of the body, offer, under our present state of ignorance, a
difficulty almost exactly parallel with that of the electric organs.
Other similar cases could be given ; for instance in plants, the very
curious contrivance of a mass of pollen-grains, borne on a foot-stalk
with an adhesive gland, is apparently the same in Orchis and
Asclepias, — genera almost as remote as is possible amongst flowering
plants ; but here again the parts are not homologous. In all cases
of beings, far removed from each other in the scale of organisation,
which are furnished with similar and peculiar organs, it will be
found that although the general appearance and function of the
organs may be the same, yet fundamental differences between them
can always be detected. For instance, the eyes of cephalopods
or cuttle-fish and of vertebrate animals appear wonderfully alike ;
and in such widely sundered groups no part of this resemblance can
be due to inheritance from a common progenitor. Mr. Mivart has
advanced this case as one of special difficulty, but I am unable to
see the force of his argument. An organ for vision must be formed
oi transparent tissue, and must include some sort cf lens fot

152 DIFFICULTIES OF THE THEORY [Chap. VI.

throwing an image at the back of a darkened chamber. Beyond
this superficial resemblance, there is hardly any real similarity
between the eyes of cuttle-fish and vertebrates, as may be seen by
cx)nsulting Hensen's admirable memoir on these organs in the
Cephalopoda. It is impossible for me here to enter on details, but
I may specify a few of the points of difference. The crystalline lens
in the higher cuttle-fish consists of two parts, placed one behind the
other like two lenses, both having a very different structure and
disposition to what occurs in the vertebrata. The retina is wholly
different, with an actual inversion of the elemental parts, and with
a large nervous ganglion included within the membranes of the
eye. The relations of the muscles are as different as it is pos-
sible to conceive, and so in other points. Hence it is not a little
difficult to decide how far even the same terms ought to be employed
in describing the eyes of the Cephalopoda and Vertebrata. It is, of
course, open to any one to deny that the eye in either case could
liave been developed through the natural selection of successive,
slight variations ; but if this be admitted in the one case, it is
clearly possible in the other ; and fundamental differences of struc-
ture in the visual organs of two groups might have been anti-
cipated, in accordance with this view of their manner of formation.
As two men have sometimes independently hit on the same
invention, so in the several foregoing cases it appears that natural
selection, working for the good of each t:>emg, and taking advan-
tage of all favourable variations, has produced similar organs, as
far as function is concerned, in distmct organic beings, which
o^ve none of their structure in common to inheritance from a
common progenitor.

Fritz MtiUer, in order to test the conclusions arrived at in this
volume, has followed out with much care a nearly similar line of
argument. Several families of crustaceans include a few species,
possessing an air-breathing apparatus and fitted to live out of the
water. In two of these families, which were more especially
examined by MUller, and which are nearly related to each other,
the species agree most closely in all important characters ; namely
in their sense-organs, circulating system, in the porition of the
tufta of hair within their complex stomachs, and [lastly in the
whole structure of the water-breathing branchiae, even to the
microscopical hooks by which they are cleansed. Hence it might
have been expected that in the few species belonging to both
families which live on the land, the equally-important air-breathing
apparatus would have been the same ; for why should this one
apparatus, g-ven for the same purpose, have been made to differ,

Chap. VI.] OF NATURAL SELECTION. loo

whilst all the other important organs were closely similar or rather
identical.

Fritz Miiller argues that this close similarity in so many points
of structure must, in accordance with the views advanced by me»
be accounted for by inhoitance from a common progenitor. Bui
as the vast majority of the species in the above two families, as
well as most other crustaceans, are aquatic in their habits, it is
improbable in the highest degree, that their common progenitor
should have been adapted for breathing air. Miiller was thus led
carefully to examine the apparatus in the air-breathing species;
and he found it to differ in each in several important points, as in
the position of the orifices, in the manner in which they are opened
and closed, and in some accessory details. Now such differences
are intelligible, and might even have been expected, on the suppo-
sition that species belonging to distinct families had slowly become
adapted to live more and more out of water, and to breathe the
air. For these species, from belonging to distinct families, would
have differed to a certain extent, and in accordance with the
principle that the nature of each variation depends on two factors,
viz. the nature of the organism and that of the surrounding con-
ditions, their variability assuredly would not have been exactly the
same. Consequently natural selection would have had different
materials or variations to work on, in order to arrive at the same
functional result ; and the structures thus acquired would almost
necessarily have differed. On the hypothesis of separate acts of
creation the whole case remains unintelligible. This line of
argument seems to have had great weight in leading Fritz Miiller
to accept the views maintained by me in this volume.

Another distinguished zoologist, the late Professor Claparede, has
argued in the same manner, and has arrived at the same result.
He shows that there are parasitic mites (Acaridas), belonging to
distinct sub- families and families, which are furnished with hair-
claspers. These organs must have been independently developed,
as they could not have been inherited from a common progenitor ;
and in the several groups they are formed by the modification of
the fore-legs, — of the iiind-legs, — of the maxillre or lips, — and of
appendages on the under side of the hind part of the body.

In the foregoing cases, we see the same end gained and the same
function performed, in beings not at all or only remotely allied, by
organs in appearance, though not in development, closely similar.
On the other hand, it is a common rule throughout nature that the
Rhine end should be gained, even sometimes in the case of closely-
reiatetl beings, by the most diversified means. How differertly

154 DIFFICULTIES OF THE THEORY Tmap. VJ,

constructed is the feathered wing of a bird and the membrane-
covered wing of a bat ; and still more so the four wings of a butter-
fly, the two wings of a fly, and the two wings with the elytra of a
beetle. Bi valve shells are made to open and shut, but on what a
number of patterns is the hinge constructed, — from the long row of
neatly interlocking teeth in a Nucula to the simple ligament of a
Mussel ! Seeds are disseminated by their minuteness,— by their
capsule being converted into a light balloon-like envelope, — by
being embedded in pulp or flesh, formed of the most diverse parts,
and rendered nutritious, as well as conspicuously coloured, so as to
attract and be devoured by birds, — by having hooks and grapnels
of many kinds and serrated awns, so as to adhere to the fur of
quadrupeds, — and by being furnished with wings and plumes, as
different in shape as they are elegant in structure, so as to be wafted
by every breeze. I will give one other instance ; for this subject of
the same end being gained by the most diversified means well
deserves attention. Some authors maintain that organic beings
have been formed in many ways for the sake of mere variety,
almost like toys in a shop, but such a view of nature is incredible.
With plants having separated sexes, and with those in which,
though hermaphrodites, the pollen does not spontaneously fall on
the stigma, some aid is necessary for their fertilisation. With
several kinds this is effected by the pollen-grains, which are light
and incoherent, being blown by the wind through mere chance on
to the stigma ; and this is the simplest plan which can well bo
conceived. An almost equally simple, though very different, plan
occurs in many plants in which a symmetrical flower secretes a fevj
deops of nectar, and is consequently visited by insects ; and these
c^rry the pollen from the anthers to the stigma.

From this simple stage we may pass through an inexhaustible
number of contrivances, all for the same purpose and effected in
essentially the same manner, but entailing changes in every part of
the flower. The nectar may be stored in variously shaped recep-
tacles, with the stamens and pistils modified in many ways, some-
times forming trap-like contrivances, and sometimes capable of
neatly adapted movements through irritability or elasticity. From
such structures we may advance till we come to such a case of
extraordinary adaptation as that lately described by Dr. Criiger in
the Coryanthes. This orchid has part of its labellum or lower lip
hoUowed out into a great bucket, into which drops of almost pure
water continually fall from two secreting horns which stand above
it ; and when the bucket is half full, the water overflows by a
spout on one side. The basal part of the labellum stands over the
bucket, and is itself hollowed out into a sort of chamber with two

Chap. VI.] OF NATURAL SELECTION. 155

lateral entrances ; within this chamber there are curious fleshy
ridges. The most ingenious man, if he had not witnessed what
takes place, could never have imagined what purpose all these parts
serve. But Dr. Criiger saw crowds of large humble-bees visiting
the gigantic flowers of this orchid, not in order to suck nectar, but
to arnaw off the ridges within the chamber above the bucket ; in
doing this they frequently pushed each other into the bucket, and
their wings being thus wetted they could not fly away, but were
compelled to crawl out through the passage formed by the spout or
overflow. Dr. Criiger saw a " continual procession " of bees thus
crawling out of their involuntary bath. The passage is narrow, and
is roofed over by the column, so that a bee, in forcing its way out,
first rubs its back against the viscid stigma and then against the
viscid glands of the pollen -masses. The pollen-masses are thus
glued to the back of the bee which first happens to crawl out
through the passage of a lately expanded flower, and are thus
carried away. Dr. Criiger sent me a flower in spirits of wine, with
a bee which he had killed before it had quite crawled out with ?»
poUen-inass still fastened to its back. When the bee, thus provided,
flies to another flower, or to the same flower a second time, and is
pushed by its comrades into the bucket and then crawls out by the
passage, the pollen-mass necessarily comes first into contact with
I he viscid stigma, and adheres to it, and the flower is fertilised.
Now at last we see the full use of every part of the flower, of the
water-secreting horns, of the bucket half full of water, which
prevents the bees from flying away, and forces them to crawl out
through the spout, and rub against the properly placed viscid pollen-
masses and the viscid stigma.

The construction of the flower in another closely allied orchid,
namely the Catasetum, is widely different, though serving the same
end ; and is equally curious. Bees visit these flowers, like those of
the Coryanthes, in order to gnaw the labellum ; in doing this they
inevitably touch a long, tapering, sensitive projection, or, as I have
called it, the antenna. This antenna, when touched, transmits a
sensation or vibration to a certain membrane which is instantly
ruptured ; this sets free a spring by which the pollen-mass is shot
forth, like an arrow, in the right direction, and adheres by its
viscid extremity to the back of the bee. The pollen-mass of the
male plant (for the sexes are separate in this orchid) is thus carried
to the flower of the female plant, where it is brought into contact
with the stigma, which is viscid enough to break certain elastic
threads, and retaining the pollen, fertilisation is effected.

How, it may be asked, in the foregoing and in ninumerable other

156 ORGANS OF LITTLE IMFORTANCE [Chap. VI.

instances, can we understand the graduated scale of complexity ajid
the multifarious means for gaining the same end. The answer no
doubt is, as already remarked, that when two forms vary, which
abeady differ from each other in some slight degree, the variability
will not be of the same exact nature, and consequently the results
obtained through natural selection for the same general purpose will
not be the same. We should also bear in mind that every highly
developed organism has passed through many changes; and that
each modified structure tends to be inherited, so that each modi-
fication will not readily be quite lost, but may be again aud again
further altered. Hence the structure of each part of each species,
for whatever purpose it may serve, is the sum of many inherited
changes, through which the species has passed during its successive
adaptations to changed habits and conditions of life.

Finally then, although in many cases it is most difficult even to
conjecture by what transitions organs have arrived at their present
state ; yet, considering how small the proportion of living and known
forms is to the extinct and unknown, I have been astonished how
rarely an organ can be named, towards which no transitional grade
is known to lead. It certainly is true, that new organs appearing
as if created for some special purpose, rarely or never appear in any
being ; — as indeed is shown by that old, but somew^hat exaggerated,
canon in natural history of " Natura non facit saltum." We meet
with this admission in the writings of almost every experienced
naturalist; or as Milne Edwards has well expressed it, Nature is
prodigal in variety, but niggard in innovation. Why, on the
theory of Creation, should there be so much variety and so little
real novelty? Why should all the parts and organs of many
independent beings, each supposed to have been separately created
for its proper place in nature, be so commonly linked together by
graduated steps ? Why should not Nature take a sudden leap
from structure to structure? On the theory of natural selection,
"we can clearly understand why she should not ; for natural
selection acts only by taking advantage of slight successive varia-
tions ; she can never take a great and sudden leap, but must
advance by short and sure, though slow steps.

Organs of little apparent Importance, as affected hy Natural

Selecticci,

As natural selection acts by life and death, — by the survival oi
the fittest, and by the destruction of the less well-fitted indi-
viduals,— 1 have sometimes felt great difficulty in understanding
the origin or formation of parts of little importance; almost as

Chap. VL] AFFECTED BY NATURAL SELECTION. 157

great, though of a very different kind, as in the case of the most
perfect and complex organs.

In the first place, we are much too ignorant in regard to the
whole economy of any one organic being, to say what slight modifi-
cations would be of importance or not. In a former chapter I have
given instances of very trifling characters, such as the clown on
fruit and the colour of its flesh, the colour of the skin and hair of
quadrupeds, which, from being correlated with constitutional
differences or from determining the attacks of insects, might
assuredly be acted on by natural selection. The tail of the giraffe
looks like an artificially constructed fly-flapper ; and it seems at
first incredible that this could have been adapted for its present
purpose by successive slight modifications, each better and better
fitted, for so trifling an object as to drive away flies ; yet we should
pause before being too positive even in this case, for we know that
the distribution and existence of cattle and other animals in South
America absolutely depend on their power of resisting the attacks
of insects : so that individuals which could by any means defend
themselves from these small enemies, would be able to range into
new pastures and thus gain a great advantage. It is not that the
larger quadrupeds are actually destroyed (except in some rare
cases) by flies, but they are incessantly harassed and their strength
reduced, so that they are more subject to disease, or not so well
enabled in a coming dearth to search for food, or to escape from
beasts of prey.

Organs now of trifling importance have probably in some cases
been of high importance to an early progenitor, and, after having
been slowly perfected at a former period, have been transmitted to
existing species in nearly the same state, although now of very
slight use ; but any actually injurious deviations in their structure
would of course have been checked by natural selection. Seeing
how important an organ of locomotion the tail is in most aquatic
animals, its general presence and use for many purposes in so
many land animals, v/hich in their lungs or modified swimbladders
betray their aquatic origin, may perhaps be thus accounted for. A
well-developed tail having been formed in an aquatic animal, it
might subsequently come to be worked in for all sorts of purposes,
— as a fly-flapper, an organ of prehension, or as an aid in turning, as
in the case of the dog, though the aid in this latter respect must be
slight, for the hare, with hardly any tail, can double still more
quickly.

In the second place, we may easily err in attributing importance
to characters, and in believing that they have been developed

158 ORGANS OF LITTLE IMPORTANCE [Ouap. VI.

through natural selection. We must by no means overlook the
effects of the definite action of changed conditions of life, — of so-
called spontaneous variations, which seem to depend in a quite
subordinate degree on the nature of the conditions, — of the ten-
dency to reversion to long-lost characters,— of the complex laws of
growth, such as of correlation, compensation, of the pressure of one
part on another, &c.,— and finally of sexual selection, by which
characters of use to one sex are often gained and then transmitted
more or less perfectly to the other sex, though of no use to this
sex. But structures thus indirectly gained, although at first of no
advantage to a species, may subsequently have b(;en taken advan-
tage of by its modified descendants, under new conditions of life
and newly acquired habits.

If green woodpeckers alone had existed, and we did not know
that there were many black and pied kinds, I dare say that we
should have thought that the green colour was a beautiful adapta-
tion to conceal this tree-frequenting bird from its enemies ; and
consequently that it was a character of importance, and had been
acquired through natural selection ; as it is, the colour is probably
in chief part due to sexual selection. A trailing palm in the Malay
Archipelago climbs the loftiest trees by the aid of exquisitely con-
structed hooks clustered around the ends of the branches, and this
contrivance, no doubt, is of the highest service to the plant ; but as we
see nearly similar hooks on many trees which are not climbers, and
which, as there is reason to believe from the distribution of the thorn-
bearing species in Africa and South America, serve as a defence
against browsing quadrupeds, so the spikes on the palm may at
first have been developed for this object, and subsequently have been
improved and taken advantage of by the plant, as it underwent
further modification and became a climber. The naked skin on the
head of a vulture is generally considered as a direct adaptation for
wallowing in putridity ; and so it may be, or it may possibly be
due to the direct action 3f putrid matter ; but we should be very
cautious in drawing any such inference, when we see that the skin
on the head of the clean-feeding male Turkey is likewise naked.
The sutures in the skulls of young mammals have been advanced aa
a beautiful adaptation for aiding parturition, and no doubt they
facilitate, or may be indispensable for this act ; but as sutures
occur in the skulls of young birds and reptiles, which have only to
escape from a broken egg, we may infer that this structure has
arisen from the laws of growth, and has been taken advantage of ir
the parturition of the higher animals.

We are profoundly ignorant of the cause of each slight varia' ion

C'HjiP. VI.] AFFECTED BY NATURAL SELECTION. 159

or individual difterence ; and we are immediately made conscions
ci" this by reflecting on the difTerences between the breeds of our
domesticated animals in different countries, — more especially in the
less civilised countries where there has been but little methodical
selection. Animals kept by savages in difterent countries often
Lave to struggle for their own subsistence, and are exposed to a
certain extent to natural selection, and individuals with slightly
dillerent constitutions would succeed best under different climates.
With cattle susceptibility to the attacks of flies is correlated with
colour, as is the liability to be poisoned by certain plants ; so that
even colour would be thus subjected to the action of natural
selection. Some observers are convinced that a damp climate
affects the growth of the hair, and that with the hair the horns are
correlated Mountain breeds always differ from lowland breeds ;
and a mountainous country would probably affect the hind limbs
from exercising them more, and possibly even the form of the
pelvis ; and then by the law of homologous variation, the front
limbs and the head would probably be affected. The shape, also,
of the pelvis might affect by pressure the shape of certain parts of
the young in the w^omb. The laborious breathing necessary in
high regions tends, as we have good reason to believe, to increase
tl^.e size of the chest ; and again correlation would come into play.
The effects of lessened exercise together with abundant food on the
whole organisation is probably still more important ; and this, as
H. von Nathusius has lately shown in his excellent Treatise, is
apparently one chief cause of the great modification which the
breeds of swine have undergone. But we are far too ignorant to specu-
late on the relative importance of the several known and unknown
causes of variation ; and I have made these remarks only to show
that, if we are unable to account for the characteristic differences
of our several domestic breeds, which nevertheless are generally
admitted to have arisen through ordinary generation from one or a
few parent-stocks, we ought not to lay too much stress on our
ignorance of the precise cause of the slight analogous differences
between true species.

Utilitarian Doctrine^ Tiowfar true : Beauty, liow acquired.

The foregoing remarks lead me to say a few words on the protest
lately made by some naturalists, against the utilitarian doctrine
that every detail of structure has been produced for the good of its
[assessor. They believe that many structures have been created
for the sake of beauty, to delight man or the Creator (but this
latter point is beyond ths scope of scientific discussion), or for the

1«0 UTILITARIAN DOCTRINE HOW FAR TRUE: [Chap. VI.

sake of mere variety, a view already discussed. Such doctrines, if
true, would be absolutely fatal to my theory. I fully admit that
many structures are now of no direct use to their possessors, and
may never have been of any use to their progenitors ; but this does
not prove that they were formed solely for beauty or variety. Nc
doubt the definite action of changed conditions, and the various
causes of modifications, lately specified, have all produced an
effect, probably a great effect, independently of any advantage thus
gained. But a still more important consideration is that the chiel
part of the organisation of every living creature is due to inherit-
ance ; and consequently, though each being assuredly is well fitted
for its place in nature, many structures have now no very close and
direct relation to present habits of life. Thus, we can hardly
believe that the webbed feet of the upland goose or of the frigate-
bird are of special use to these birds ; we cannot believe that the
similar bones in the arm of the monkey, in the fore-leg of the
horse, in the wing of the bat, and in the flipper of the seal, are of
special use to these animals. We may safely attribute these
structures to inheritance. But webbed feet no doubt were as
useful to the progenitor of the upland goose and of the frigate-bird,
as they now are to the most aquatic of living birds. So we may
believe that the progenitor of the seal did not possess a flipper, but
a foot with five toes fitted for walking or grasping ; and we may
further venture to believe that the several bones in the limbs of
the monkey, horse, and bat, were originally developed, on the
principle of utility, probably through the reduction of more
numerous bones in the fin of some ancient fish-like progenitor of
the whole class. It is scarcely possible to decide how much
allowance ought to be made for such causes of change, as the
definite action of external conditions, so-called spontaneous varia-
tions, and the complex laws of growth ; but v/ith these important
exceptions, we may conclude that the structure of every living
creature either now is, or was formerly, of some direct or in-
direct use to its possessor.

With respect to the belief that organic beings have been created
beautiful for the delight of man, — a belief which it has been pro-
nounced is subversive of my whole theory, — I may first remark
that the sense of beauty obviously depends on the nature of the
mind, irrespective of any real quality in the admired object ; and
that the idea of what is beautiful, is not innate or unalterable.
We see this, for instance, in the men of different races admiring an
entirely different standard of beauty in their women. If beautiful
objects had been created solely for man's gratification, it ought to

Chap. VI.] BEAUTY HOW ACQUIRED. 161

be shown that before man appeared, there was less beauty on the
face of the earth than since he came on the stage. Were the beau-
tiful volute and cone shells of the Eocene epoch, and the gracefully
Bculptui'ed ammonites of the Secondary period, created that man
might ages afterwards admire them in his cabinet ? Few objects
are more beautiful than the minute siliceous cases of the diato-
macese: were these created that they might be examined and
admired under the higher powers of the microscope ? The beauty
in this latter case, and in many others, is apparently wholly due
to symmetry of growth. Flowers rank amongst the most beautiful
productions of nature ; but they have been rendered conspicuous
in contrast with the green leaves, and in consequence at the same
time beautiful, so that they may be easily observed by insects. I
have come to this conclusion from finding it an invariable rule that
when a flower is fertihsed by the wind it never has a gaily-coloured
corolla. Several plants habitually produce two kinds of flowers ;
one kind open and coloured so as to attract insects; the other
closed, not coloured, destitute of nectar, and never visited by insects.
Hence we may conclude that, if insects had not been developed on the
face of the earth, our plants would not have been decked with beau-
tiful flowers, but would have produced only such poor flowers as we
see on our flr, oak, nut and ash trees, on grasses, spinach, docks, and
nettles, which are all fertilised through the agency of the wind. A
similar line of argument holds good with fruits ; that a ripe straw-
berry or cherry is as pleasing to the eye as to the palate, — that the
gaily-coloured fruit of the spindle-wood tree and the scarlet berries
of the holly are beautiful objects, — will be admitted by every one,,
But this beauty serves merely as a guide to birds and beasts, in
order that the fruit may be devoured and the manured seeds dis-
seminated : I infer that this is the case from having as yet found
no exception to the rule that seeds are always thus disseminated
when embedded within a fruit of any kind (that is within a fleshy
or pulpy envelope), if it be coloure<l of any brilliant tint, or ren-
dered conspicuous by being white or black.

On the other hand, I willingly admit that a great number of
male animals, as all our most gorgeous birds, some fishes, reptiles,
and mammals, and a host of magnificently coloured butterflies,
have been rendered beautiful for beauty's sake ; but this has been
eifected through sexual selection, that is, by the more beautiful
males having been continually preferred by the females, and^not for
the delight of man. So it is with the music of birds. We may
inff from all this that a nearly similar taste for beautiful colours
and for musical sounds runs through a large part of the animal

M

162 UTILITARIAN DOCTRINE HOW FAR TRUE' [Chap. VI.

kingdom. When the female is as beautifully coloured as the male,
which is not rarely the case with birds and butterflies, the cause
apparently lies in the colours acquired through sexual selection
having been transmitted to both sexes, instead of to the males
alone. How the sense of beauty in its simplest form — that is, the
reception of a peculiar kind of pleasure from certain colours, forms ,
and sounds — was first developed in the mind of man and of the lower
animals, is a very obscure subject. The same sort of difficulty is
presented, if we enquire how it is that certain flavours and odours
give pleasure, and others displeasure. Habit, in all these cases
appears to have come to a certain extent into play ; but there must
be some fundamental cause in the constitution of the nervous
system in each species.

Natural selection cannot possibly produce any modification in
a species exclusively for the good of another species ; though
throughout nature one species incessantly takes advantage of, and
profits by, the structures of others. But natural selection can
and does often produce structures for the direct injury of other
animals, as we see in the fang of the adder, and in the ovipositor
of the ichneumon, by which its eggs are deposited in the living
bodies of other insects. If it could be proved that any part of
the structure of any one species had been formed for the exclusive
good of another species, it would annihilate my theory, for such
could not have been produced through natural selection. Although
many statements may be found in works on natural history to this
effect, I cannot find even one which seems to me of any weight.
It is admitted that the rattlesnake has a poison-fang for its own
defence, and for the destruction of its prey; but some authors
suppose that at the same time it is furnished with a rattle for its own
injury, namely, to warn its prey. I would almost as soon believe
that the cat curls the end of its tail when preparing to spring, in
order to warn the doomed mouse. It is a much more probable
view that the rattlesnake uses its rattle, the cobra expands its frilly
and the puff-adder swells whilst hissing so loudly and harshly, in
order to alarm the many birds and beasts which arc known to
attack even the most venomous species. Snakes act on the same
principle which makes the hen ruffle her feathers and expand her
wings when a dog approaches her chickens ; but I have not space
hsreto enlarge on the many ways by which animals endeavour to
frighten away their enemies.

Natural selection will never produce in a being any structure
more injurious than, beneficial to that being, for natural selection

Chap. VI.] UTILITARIAN DOCTRINE HOW FAR TRUE. 163

acts solely by and for the good of each. No organ will be formed
as Paley has remarked, for the purpose of causing pain or for doinf»
an injury to its possessor. If a fair balance be struck between the
good and evil caused by each part, each will be found on the whole
advantageous. After the lapse of time, under changing conditions
of life, if any part comes to be injurious, it will be modified ; or if it
be not so, the being will become extinct as myriads have become
extinct.

Natural selection tends only to make each organic being as
perfect as, or slightly more perfect than, the other inhabitants of the
same country with which it comes into competition. And we see
that this is the standard of perfection attained under natm'e. The
endemic productions of New Zealand, for instance, are perfect one
compared with another ; but they are now rapidly yielding before
the advancing legions of plants and animals introduced from Europe.
Natural selection will not produce absolute perfection, nor do we
always meet, as far as we can judge, with this high standard under
nature. The correction for the aberration of light is said by Miiller
not to be perfect even in that most perfect organ, the human eye.
Helmholtz, whose judgment no one will dispute, after describing
in the strongest terms the wonderful powers of the human eye,
adds these remarkable words : " That which we have discovered
in the way of inexactness and imperfection in the optical machine
and in the image on the retina, is as nothing in comparison with the
incongruities which we have just come across in the domain of the
sensations. One might say that nature has taken delight in accu-
mulating contradictions in order to remove all foundation from the
theory of a pre-existing harmony between the external and internal
worlds." If our reason leads us to admire with enthusiasm a
multitude of inimitable contrivances in nature, this same reason
tells us, though we may easily err on both sides, that some other
contrivances are less perfect. Can we consider the sting of the bee
as perfect, which, when used against many kinds of enemies,
cannot be withdrawn, owing to the backward serratures, and thus
inevitably causes the death of the insect by tearing out its viscera ?

If we look at the sting of the bee, as having existed in a remote
progenitor as a boring and serrated instrument, like that in so many
members of the same great order, and that it has since been modi-
fied but not perfected for iis present purpose, with the poison origi-
nally adapted for some other object, such as to produce galls, since
intensified, we can perhaps understand how it is that the use of the
sting should so often cause the insect's own death: for if on
the whole the power of stinging be useful to the social commimity,

M 2

164 SUMMARY. [Chap. YL

it will fulfil all the requirements of natural selection, though it may
cause the death of some few members. If we admire the truly
wonderful power of scent by which the males of many insects find
their females, can we admire the production for this single purpose
of thousands of drones, which are utterly useless to the community
for any other purpose, and which are ultimately slaughtered by
their industrious and sterile sisters ? It may be difficult, but we
ou^^ht to admire the savage instinctive hatred of the queen-bee,
which urges her to destroy the young queens, her daughters, as soon
as they are born, or to perish herself in the combat ; for undoubtedly
this is for the good of the community ; and maternal love or ma-
ternal hatred, though the latter fortunately is most rare, is all the
same to the inexorable principle of natural selection. If we admire
the several ingenious contrivances, by which orchids and many other
plants are fertilised through insect agency, can we consider as
equally perfect the elaboration of dense clouds of pollen by our
fir-trees, so that a few granules may be wafted by chance on to the
ovules ?

Summary : the Law of Unity of Type and of the Conditions of
Existence embraced hy the Theory of Natural Selection.

We have in this chapter discussed some of the difficulties and
objections which may be urged against the theory. Many of them
are serious ; but I think that in the discussion light has been thrown
on several facts, which on the belief of independent acts of creation
are utterly obscure. We have seen that species at any one period
are not indefinitely variable, and are not linked together by a
multitude of intermediate gradations, partly because the process of
natural selection is always very slow, and at any one time acts only
on a few forms; and partly because the very process of natural
selection implies the continual supplanting and extinction of pre-
ceding and intermediate gradations. Closely allied species, now
living on a continuous area, mus.t often have been formed when the
area was not continuous, and when the conditions of life did not
insensibly graduate away from one part to another. When two
varieties are formed in two districts of a continuous area, an inter-
mediate variety will often be formed, fitted for an intermediate
sone ; but from reasons assigned, the intermediate variety will
usually exist in lesser numbers than the two forms which it
connects ; consequently the two latter, during the course of further
modification, from existing in greater numbers, will have a great
advantage over the less numerous intermediate variety, and will
thus generally succeed in supplanting and exterminating it.

Chap. VI.] SUMMARY. 165

We have seen in this chapter how cautious we should be in con-
dading that the most different habits of life could not graduato
into each other; that a bat, for instance, could not have been
formed by natural selection from an animal which at first only-
glided through the au*.

We have seen that a species under new conditions of life may
change its habits ; or it may have diversified habits, with some
very unlike those of its nearest congeners. Hence we can under-
stand, bearing in mind that each organic being is trying to live
wherever it can live, how it has arisen that there are upland geese
with webbed feet, ground woodpeckers, diving thrushes, and petrels
with the habits of auks.

Although the belief that an organ so perfect as the eye could
have been formed by natural selection, is enough to stagger any
one ; yet in the case of any organ, if we know of a long series of
gradations in complexity, each good for its possessor, then, under
changing conditions of life, there is no logical impossibility in the
acquirement of any conceivable degree of perfection through natural
selection. In the cases in which we know of no intermediate or
transitional states, we should be extremely cautious in concluding
that none can have existed, for the metamorphoses of many organs
show what wonderful changes in function are at least possible. For
instance, a swimbladder has apparently been converted into an air-
breathing lung. The same organ having performed simultaneously
very different functions, and then having been in part or in whole
specialised for one function ; and two distinct organs having per-
formed at the same time the same function, the one having been
perfected whilst aided by the other, must often have largely facili-
tated transitions.

We have seen that in two beings widely remote from each other
in the natural scale, organs serving for the same purpose and in
external appearance closely similar may have been separately and
independently formed ; but when such organs are closely examined,
essential differences in their structure can almost always be detected;
and this naturally follows from the principle of natural selection.
On the other hand, the common rule throughout nature is infinito
diversity of structure for gaining the same end ; and this again
naturally follows from the same great principle.

In many cases we are far too ignorant to be enabled to assert that
a part or organ is so unimportant for the welfare of a species, that
modifications in its structure could not have been slowly accumu-
lated by means of natural selection. In many other cases, moaifl-

1G6 SUMMARY. [Chap. VL

cations are probably the direct result of the laws of variation or oi
growth, independently of any good having been thus gained. But
even such structures have often, as we may feel assured, been
subsequently taken advantage of, and still further modified, for the
good of species under new conditions of life. We may, also, believe
that a jjart formerly of high importance has frequently been re-
tained (as the tail of an aquatic animal by its terrestrial descend-
ants), though it has become of such small importance that it could
not, in its present state, have been acquired by means of natural
selection.

Natural selection can produce nothing in one species for the
exclusive good or injury of another ; though it may well produce
parts, organs, and excretions highly useful or (;ven indispensable, or
again highly injurious to another species, but in all cases at the
same time useful to the possessor. In each well-stocked country
natural selection acts through the competition of the inhabitants,
and consequently leads to success in the battle for life, only in
accordance with the standard of that particular country. Hence
the inhabitants of one country, generally the smaller one, often
yield to the inhabitants of another and generally the larger country.
For in the larger country there will have existed more individuals
and more diversified forms, and the competition will have been
severer, and thus the standard of perfection will have been rendered
higher. Natural selection will not necessarily lead to absolute
perfection ; nor, as far as we can judge by our limited faculties, can
absolute perfection be everywhere predicated.

On the theory of natural selection we can clearly understand the
full meaning of that old canon in natural history, "Natura non
facit saltum." This canon, if we look to the present inhabitants
alone of the world, is not strictly correct ; but if we include all
those of past times, whether known or unknown, it must on this
theory be strictly true.

It is generally acknowledged that all organic beings have been
formed on two great laws— Unity of Type, and the Conditions of
Existence. By unity of type is meant that fimdamental agreement
in structure which we see in organic beings of the same class, and
which is quite independent of their habits of life. On my theory,
tmity of type is explained by unity of descent. The expression of
conditions of existence, so often insisted on by the illustrious
Cuvier, is fully embraced by the principle of natural selection. For
natural selection acts by either now adapting the varying parts of
each being to its organic and inorganic conditions of life ; or by

Chap. VI.j SUMMARY. 167

having adapted them during past periods of time : the adaptations
being aided in many cases by the increased use or disuse of parts,
being affected by the direct action of the external conditions of
life, and subjected in all cases to the several laws of growth and
variation. Hence, in fact, the law of the Conditions of Existence is
the higher law ; as it includes, through the inheritance of former
variations and adaptations, that of Unity of Type.

170 ]\IISCELLANEOUS OBJECTIONS TO THE [CuAr. VII

iu single characters, but in many parts ; and lie asks, how it always
comes that many parts of the organisation should have been modi-
fied at the same time through variation and natural selection J
But there is no necessity for supposing that all the parts of any
being have been simultaneously modified. The most striking
modifications, excellently adapted for some purpose, might, as was
formerly remarked, be acquired by successive variations, if slight,
first in one part and then in another ; and as they would be trans-
mitted all together, they would appear to us as if they had been
simultaneously developed. The best answer, however, to the above
objection is afforded by those domestic races which have been
modified, chiefly through man's power of selection, for some special
pu-rpose. Look at the race and dray horse, or at the greyhound
and mastiff. Their whole frames and even their mental characteristics
have been modified ; but if we could trace each step in the history
of their transformation, — and the latter steps can be traced, — we
should not see great and simultaneous changes, but first one part
and then another slightly modified and improved. Even when
selection has been applied by man to some one character alone,
— of which our cultivated plants ofier the best instances, — it will
invariably be found that although this one part, whether it be the
flower, fruit, or leaves, has been greatly changed, almost all the
other parts have been slightly modified. This may be attributed
partly to the principle of correlated growth, and partly to so-called
spontaneous variation.

A much more serious objection has been urged by Bronn, and
recently by Broca, namely, that many characters appear to be of no
service whatever to their possessors, and therefore cannot have been
influenced through natural selection. Bronn adduces the length of
the ears and tails in the different species of hares and mice, — the
complex folds of enamel in the teeth of many animals, and a
multitude of analogous cases. With respect to plants, this subject
has been discussed by Nageli in an admirable essay. He admits that
natural selection has effected much, but he insists that the families
of plants differ chiefly from each other in morphological characters,
which appear to be quite unimportant for the welfare of the species.
He consequently believes in an innate tendency towards progressive
and more perfect development. He specifies the arrangement of the
cells in the tissues, and of the leaves on the axis, as cases in which
natural selection could not have acted. To these may be added
the numerical divisions in the parts of the flower, the position
of the ovules, the shape of the seed, when not of any use for dis-
eemination, &c.

CHAP. VII.] THEORY OF NATURAL SELECTION. 171

There is much force in the above objection. Nevertheless, we
ought, in the first place, to be extremely cautious in pretending
to decide what structures now are, or have formerly been, of use to
each species. In the second place, it should always be borne in
mind that when one part is modified, so will be other parts, through
certain dimly seen causes, such as an increased or diminished flow
of nutriment to a part, mutual pressure, an early developed part
affecting one subsequently developed, and so forth, — as well as
through other causes which lead to the many mysterious cases
of correlation, which we do not in the least understand. These
agencies may be all grouped together, for the sake of brevity, under
the expression of the laws of growth. In the third place, we have
to allow for the direct and definite action of changed conditions of
life, and for so-called spontaneous variations, in which the nature
of the conditions apparently plays a quite subordinate part. Bud-
variations, such as the appearance of a moss-rose on a common
rose, or of a nectarine on a peach-tree, offer good instances of spon-
taneous variations ; but even in these cases, if we bear in mind the
power of a minute drop of poison in producing complex galls, we
ought not to feel too sure that the above variations are not the
effect of some local change in the nature of the sap, due to some
change in the conditions. There must be some efficient cause for
each slight individual difference, as well as for more strongly
marked variations which occasionally arise ; and if the unknown
cause were to act persistently, it is almost certain that all the
individuals of the species would be similarly modified.

In the earlier editions of this work I under-rated, as it now seems
probable, the frequency and importance of modifications due to
spontaneous variability. But it is impossible to attribute to this
cause the innumerable structures which are so well adapted to the
habits of life of each species. I can no more beheve in this, than
that the well-adapted form of a race^-horse or greyhound, which
before the principle of selection by man was well understood, excited
so much surprise in the minds of the older naturalists, can thus be
explained.

It may be worth while to illustrate some of the foregoing remarks.
With respect to the assumed inutility of various parts and organs,
H is hardly necessary to observe that even in the higher and best-
known animals many structures exist, which are so highly developed
that no one doubts that they are of importance, yet their use has
not been, or has only recently been, ascertained. As Bronn gives
the length of the ears and tail in the several species of mice as
instances, though trifling ones, of differences in structure which can

172 MISCELLANEOUS OBJECnONS TO THE [Cuaf. VII.

be of no special use, I may mention that, according to Dr. Schobl,
the external ears of the common mouse are supplied in an extra-
ordinary manner with nerves, so that they no doubt serve as tactile
organs ; hence the length of the ears can hardly be quite unim-
portant. Wo shall, also, presently see that the tail is a highly
useful prehensile organ to some of the species ; and its use would
be mnch influenced by its length.

With respect to plants, to which on account of Nageli's essay
I shall confine myself in the following remarks, it will be admitted
that the flowers of orchids present a multitude of curious structures,
which a few years ago would have been considered as mere morpho-
locrical differences without any special function ; but they are now
known to be of the highest importance for the fertilisation of the
species through the aid of insects, and have probably been gained
through natural selection. No one until lately would have imagined
that in dimorphic and trimorphic plants the different lengths of the
stamens and pistils, and their arrangement, could have been of any
service, but now we know this to be the case.

In certain whole groups of plants the ovules stand erect, and in
others they are suspended ; and within the same ovarium of some
few plants, one ovule holds the former and a second ovule the latter
position. These positions seem at first purely morphological, or
of no physiological signification ; but Dr. Hooker informs me that
within the same ovarium, the upper ovules alone in some cases,
and in other cases the lower ones alone are fertilised ; and he
suggests that this probably depends on the direction in which the
pollen-tubes enter the ovarium. If so, the position of the ovules,
even when one is erect and the other suspended within the same
ovarium, would follow from the selection of any slight deviations in
position which favoured their fertilisation, and the production of seed.

Several plants belonging to distinct orders habitually produce
flowers of two kinds, — the one open of the ordinary structure, the
other closed and imperfect. These two kinds of flowers sometimes
differ wonderfully in structure, yet may be seen to graduate into
each other on the same plant. The ordinary and open flowers can
be intercrossed ; and the benefits which certainly are derived from
this process are thus secured. The closed and imperfect flowers are,
however, manifestly of high importance, as they yield with the
utmost safety a large stock of seed, with the expenditure of wonder-
fully little pollen. The two kinds of flowers often differ much, aa
just stated, in structure. The petals in the imperfect flowers almost
always consist of mere rudiments, and the pollen-grains are reduced
in diameter. In Ononis columna3 five of the alternate stamens aro

Chap. VII.] THEORY OF NATURAL SELECTION. 173

rudimentary ; and in some species of Viola three stamens are in
this state, two retaining their proper function, but being of very
small size. In six out of thirty of the closed flowers in an Indian
violet (name unknown, for the plants have never produced with me
perfect flowers), the sepals are reduced from the normal number
of five to three. In one section of the MalpighiacejB the closed
flowers, according to A. de Jussieu, are still further modified, for
the five stamens which stand opposite to the sepals are all aborted,
a sixth stamen standing opposite to a petal being alone developed ;
and this stamen is not present in the ordinary flowers of these
species ; the style is aborted ; and the ovaria are reduced from three
to two. Now although natural selection may well have had the
power to prevent some of the flowers from expanding, and to reduce
the amount of pollen, when rendered by the closure of the flowers
superfluous, yet hardly any of the above special modifications can
have been thus determined, but must have followed from the laws of
growth, including the functional inactivity of parts, during the pro-
gress of the reduction of the pollen and the closure of the flowers.

It is so necessary to appreciate the important efiects of the laws
of growth, that I will give some additional cases of another kind,
namely of differences in the same part or organ, due to differences
in relative position ou the same plant. In the Spanish chestnut,
and in certain fir-trees, the angles of divergence of the leaves differ,
according to Schacht, in the nearly horizontal and in the upright
branches. In the common rue and some other plants, one flower,
usually the central or terminal one, opens first, and has five sepals
and petals, and five divisions to the ovarium ; whilst all the other
flowers on the plant are tetramerous. In the British Adoxa the
uppermost flower generally has two calyx-lobes with the other
organs tetramerous, whilst the surrounding flowers generally have
three calyx-lobes with the other organs pentamerous. In many
Compositse and Umbelliferse (and in some other plants) the circum-
ferential flowers have their corollas much more developed than those
of the centre ; and this seems often connected with the abortion of the
reproductive organs. It is a more curious fact, previously referred
to, that the achenes or seeds of the circumference and centre
sometimes differ greatly in form, colour, and other characters. In
Carthamus and some other Compositse the central achenes alone
are furnished with a pappus ; and in Hyoseris the same head yields
achenes of three different forms. In certain Umbelliferse the ex-
terior seeds, according to Tausch, are orthospermous, and the central
one coslospermous, and this is a character which was considered by
De Candolle to be in other species of the highest systematic im-

174 MISCELLANEOUS OBJECTIONS TO THE [Chap. VIL

portance. Prof. Braun mentions a Fumariaceous genus, in wliich
the flowers in the lower part of the spike bear oval, ribbed, one-
seeded nutlets ; and in the upper part of the spike, lanceolate, two-
valved, and two-seeded siliques. In these several cases, with the
exception of that of the well developed ray-florets, which are of service
in making the flowers conspicuous to insects, natural selection can-
not, as far as we can judge, have come into play, or only in a quite
subordinate manner. All these modifications follow from the relative
position and inter-action of the parts ; and it can hardly be doubted
that if all the flowers and leaves on the same plant had been sub-
jected to the same external and internal condition, as are the flowers
and leaves in certain positions, all would have been modified in the
same manner.

In numerous other cases we find modifications of structure, which
are considered by botanists to be generally of a highly import-
ant nature, affecting only some of the flowers on the same plant,
or occurring on distinct plants, which grow close together under the
same conditions. As these variations seem of no special use tc
the plants, they cannot have been influenced by natural selection.
Of their cause we are quite ignorant; we cannot even attribute
them, as in the last class of cases, to any proximate agency, such
as relative position. I will give only a few instances. It is so
common to observe on the same plant, flowers indifferently tetra-
merous, pentamerous, &c., that I need not give examples; but as
numerical variations are comparatively rare when the parts are
few, I may mention that, according to De Candolle, the flowers or
Papaver bracteatum offer either two sepals with four petals (which
is the common type with poppies), or three sepals with six petals.
The manner in which the petals are folded in the bud is in most
groups a very constant morphological character ; but Professor Asa
Gray states that with some species of Mimulus, the aestivation is
almost as frequently that of the Ehinanthidea3 as of the Antirrhi-
nidese, to which latter tribe the genus belongs. Aug. St. Hilaire
gives the following cases : the genus Zanthoxylon belongs to a
division of the Eutacese with a single ovary, but in some species
flowers may be found on the same plant, and even in the same
panicle, with either one or two ovaries. In Helianthemum the
capsule has been described as unilocular or 3-locular; and in
H. mutabile, "Une lame, jplus ou moins large, s'etend entre le
pericarpe et le placenta." In the flowers of Saponaria officinalis,
Dr. Masters has observed instances of both marginal and free central
placentation. Lastly, St. Hilaire found towards the southern ex-
treme of the range of Gomphia ole^formis two forms which he did

Chap. VII.] THEORr OF NATURAL SELECTION. 175

not at first doubt were distinct species, but lie subsequently saw
them growing on the same bush ; and he then adds, " Voilk done
dans im mgme individu des loges et un style qui se rattachent
tantot h un axe verticale et tantot k un gynobase."

We thus see that with plants many morphological changes may
be attributed to the laws of growth and the inter-action of parts,
independently of natural selection. But with respect to Nageli's
doctrine of an innate tendency towards perfection or progressive
development, can it be said in the case of these strongly pro-
nounced variations, that the plants have been caught in the act of
progressing towards a higher state of development ? On the con •
trary, I should infer from the mere fact of the parts in question
differing or varying greatly on the same plant, that such modi-
fications were of extremely small importance to the plants them-
selves, of whatever importance they may generally be to us for
our classifications. The acquisition of a useless part can hardly
be said to raise an organism in the natural scale ; and in the case
of the imperfect, closed flowers above described, if any new prin-
ciple has to be invoked, it must be one of retrogression rather than
of progression ; and so it must be with many parasitic and degraded
animals. We are ignorant of the exciting cause of the above
specified modifications ; but if the unknown cause were to act
almost uniformly for a length of time, we may infer that the result
would be almost uniform ; and in this case all the individuals of the
species would be modified in the same manner.

From the fact of the above characters being unimportant for the
welfare of the species, any slight variations which occurred in them
would not have been accumulated and augmented through natural
selection. A structure which has been developed through loug-
continued selection, when it ceases to be of service to a species,
generally becomes variable, as we see with rudimentary organs ; for
it will no longer be regulated by this same power of selection.
But when, from the nature of the organism and of the conditions,
modifications have been induced which are unimportant for the
welfare of the species, they may be, and apparently often have
been, transmitted in nearly the same state to numerous, otherwise
modified, descendants. It cannot have been of much importance
to the greater number of mammals, birds, or reptiles, whether they
were clothed with hair, feathers, or scales ; yet hair has been trans-
mitted to almost all mammals, feathers to all birds, and scales to
all true reptiles. A structure, whatever it may be, which is com-
mon to many allied forms, is ranked by us as of high systematic
importance, and consequently is often assumed to be of high vi tal

176 MISCELLANEOUS OBJECTIONS TO THE [Chap. Vlt

importance to the species. Thus, as I am inclined to believe,
morphological diflferences, which we consider as important — snch aji
the arrangement of the leaves, the divisions of the flower or of the
ovarimn, the position of the ovules, &c. — first appeared in many
cases as fluctuating variations, which sooner or later became con-
stant through the nature of the organism and of the surrounding
conditions, as well as through the intercrossing of distinct indivi-
duals, but not through natural selection ; for as these morphological
characters do not affect the welfare of the species, any slight devia-
tions in them could not have been governed or accumulated through
this latter agency. It is a strange result which we thus arrive at,
namely that characters of slight vital importance to the species,
are the most important to the systematist ; but, as we shall here-
after see when we treat of the genetic principle of classification,
this is by no means so paradoxical as it may at first appear.

Although we have no good evidence of the existence in organic
beings of an innate tendency towards progressive development, yet
this necessarily follows, as I have attempted to show in the fourth
chapter, through the continued action of natural selection. For the
best definition which has ever been given of a high standard of
organisation, is the degree to which the parts have been specialised
or differentiated ; and natural selection tends towards this end, inas-
much as the parts are thus enabled to perform their functions more
efficiently.

A distinguished zoologist, Mr. St. George Mivart, has recently
collected all the objections which have ever been advanced by
myself and others against the theory of natural selection, as pro-
pounded by Mr. Wallace and myself, and has illustrated them with
admirable art and force. When thus marshalled, they make a
formidable array ; and as it forms no part of Mr. Mivart's plan to
give the various facts and considerations opposed to his conclusions,
no slight effort of reason and memory is left to the reader, who may
wish to weigh the evidence on both sides. When discussing special
cases, Mr. Mivart passes over the effects of the increased use and
disuse of parts, which I have always maintained to be highly im-
portant, and have treated in my * Variation under Domestication '
at greater length than, as I believe, any other writer. Ho likewise
often assumes that I attribute nothing to variation, independently
of natural selection, whereas in the work just referred to I have
collected a greater number of well-established cases than can be
found in any other work known to me. My judgment may not be
trnatworthy, but after reading with care Mr. Mivart's book» and

t'liAP. VII.] THEORY OF NATURAL SELECTION. IT 7

comparing each section with what I have said on the same heacL
I never before felt so strongly convinced of the general truth of the
conclusions here arrived at, subject, of course, in so intricate a
subject, to much partial error.

All Mr. Mivart's objections will be, or have been, considered in
the present volume. The one new point which appears to have
struck many readers is, " that natural selection is incompetent to
account for the incipient stages of useful structures." This subject
is intimately connected with that of the gradation of characters,
often accompanied by a change of function, — for instance, the con-
version of a swim-bladder into lungs, — points which were discussed
in the last chapter under two headings. Nevertheless, I will here
consider in some detail several of the cases advanced by Mr. Mivart,
selecting those which are the most illustrative, as want of space
prevents me from considering all.

The giraffe, by its lofty stature, much elongated neck, fore-legs,
head and tongue, has its whole frame beautifully adapted for
browsing on the higher branches of trees. It can thus obtain food
beyond the reach of the other Ungulata or hoofed animals inhabiting
the same country ; and this must be a great advantage to it during
dearths. The Niata cattle in S. America show us how small a
difference in structure may make, during such periods, a great differ-
ence in preserving an animal's life. These cattle can browse as well
as others on grass, but from the projection of the lower jaw they
cannot, during the often recurrent droughts, browse on the twigs
of trees, reeds, &c,, to which food the common cattle and horses
are then driven ; so that at these times the Niatas perish, if not fed
by their owners. Before coming to Mr. Mivart's objections, it may
be well to explain once again how natural selection will act in all
ordinary cases. Man has modified some of his animals, without
necessarily having attended to special points of structure, by simply
preserving and breeding from the fleetest individuals, as with the
race-horse and greyhound, or as with the game-cock, by breeding
from the victorious birds. So under nature with the nascent giraffe,
the individuals which were the highest browsers and were able
during dearths to reach even an inch or two above the others, will
often have been preserved; for they will have roamed over the
whole country in search of food. That the individuals of the same
species often differ slightly in the relative lengths of all their parts
may be seen in many works of natural history, in which careful
measurements are given. These shght proportional differences, due
to the laws of growth and variation, are not of the slightest use or
importance to most species. But it will have been otherwise with

178 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII.

the nascent giraffe, considering its probable habits of Ufe ; for those
individuals which had some one part or several parts of their bodies
rather more elongated than usual, would gen-erally have survived.
These will have intercrossed and left offspring, either inheriting the
same bodily pecuUarities, or with a tendency to vary again in the
same manner ; whilst the individuals, less favoured in the same
respects, will have been the most liable to perish.

We here see that there is no need to separate single pairs, as man
does, when he methodically improves a breed : natural selection will
preserve and thus separate all the superior individuals, allowing
them freely to intercross, and will destroy all the inferior indivi-
duals. By this process long-continued, which exactly corresponds
with what I have called unconscious selection by man, combined no
doubt in a most important manner with the inherited effects of the
increased use of parts, it seems to me almost certain that an ordinary
hoofed quadruped might be converted into a giraffe.

To this conclusion Mr. Mivart brings forward two objections.
One is that the increased size of the body would obviously require
an increased supply of food, and he considers it as "very problemati-
cal whether the disadvantages thence arising would not, in times of
scarcity, more than counterbalance the advantages." But as the
giraffe does actually e"xist in large numbers in S. Africa, and as
some of the largest antelopes in the world, taller than an ox, abound
there, why should we doubt that, as far as size is concerned, inter-
mediate gradations could formerly have existed there, subjected as
now to severe dearths. Assuredly the being able to reach, at each
stage of increased size, to a supply of food, left untouched by the
other hoofed quadrupeds of the country, would have been of some
advantage to the nascent giraffe. Nor must we overlook the fact,
that increased bulk would act as a protection against almost all
beasts of prey excepting the lion ; and against this animal, its tall
neck, — and the taller the better, — would, as Mr. Chauncey Wright
iias remarked, serve as a watch-tower. It is from this cause, as Sir
S. Baker remarks, that no animal is more difficult to stalk than the
giraffe. This animal also uses its long neck as a means of offence
or defence, by violently swinging its head armed with stump-like
horns. The preservation of each species can rarely be determined
by any one advantage, but by the union of all, great and small.

Mr. Mivart then asks (and this is his second objection), if natural
selection be so potent, and if high browsing be so great an advan-
tage, why has not any other hoofed quadruped acquired a long neck
and lofty statui'e, besides the giraffe, and, in a lesser degree, the
camel, guanaco, and macrauchenia ? Or, again, why has not any

Chap. VIL] THEORY OF NATURAL SELECTION. 179

member of the group acquired a long proboscis ? With respect to
S. Africa, which was formerly inhabited by numerous herds of the
giraffe, the answer is not difficult, and can best be given by an
illustration. In every meadow in England in which trees grow,
we see the lower branches trimmed or planed to an exact level by
the browsing of the horses or cattle ; and what advantage would it
be, for instance, to sheep, if kept there, to acquire slightly longer
necks? In every district some one kind of animal will almost
certainly be able to browse higher than the others ; and it is almost
equally certain that this one kind alone could have its neck
elongated for this purpose, through natural selection and the effects
of increased use. In S. Africa tjie competition for browsing on the
higher branches of the acacias and other trees must be between
giraffe and giraffe, and not with the other ungulate animals.

Why, in other quarters of the world, various animals belonging
to this same order have not acquired either an elongated neck
or a proboscis, cannot be distinctly answered; but it is as un-
reasonable to expect a distinct answer to such a question, as
why some event in the history of mankind did not occur in one
country, whilst it did in another. We are ignorant with respect to
the conditions which determine the numbers and range of each
species ; and we ca^nnot even conjecture what changes of structure
would be favourable to its increase in some new country. We can,
however, see in a general manner that various causes might have
interfered with the development of a long neck or proboscis. To
reach the foliage at a considerable height (without climbing, for
which hoofed animals are singularly ill-constructed) implies greatly
increased bulk of body; and we know that some areas support
singularly few large quadrupeds, for instance S. America, though it
is so luxuriant ; whilst S. Africa abounds with them to an un-
paralleled degree. Why this should be so, we do not know ; nor
why the later tertiary periods should have been much more favour-
able for their existence than the present time. Whatever the
fauses may have been, we can see that certain districts and times
would have been much more favourable than others for the develop-
ment of so large a quadruped as the giraffe.

In order that an animal should acquire some structure specially
and largely developed, it is almost indispensable that several other
parts should be modified and co-adapted. Although every part of
the body varies slightly, it does not follow that the necessary parts
should always vary in the right direction and to the right degree.
With the different species of our domesticated animals we kno^
that the parts vary in a different manner and degree; and that

N 2

180 MISCELLANEOUS OBJECTIONS TO THE [Chap. YIl.

some species are much more variable than, others. Even if the
fitting variations did arise, it does not follow that natural selection
would be able to act on them, and produce a structure which ap-
parently would be beneficial to the species. For instance, if the
number of individuals existing in a country is determined chiefly
through destruction by beasts of prey,— by external or internal
parasites, &c., — as seems often to be the case, then natural selection
will be able to do little, or will be greatly retarded, in modifying
any particular structure for obtaining food. Lastly, natural selec-
tion is a slow process, and the same favourable conditions must
long endure in order that any marked effect should thus be pro-
duced. Except by assigning such general and vague reasons, we
cannot explain why, in many quarters of the world, hoofed quadru-
peds have not acquired much elongated necks or other means for
browsing on the higher branches of trees.

Objections of the same nature as the foregoing have been advanced
by many writers. In each ca&e various causes, besides the general
ones just indicated, have probably interfered with the acquisition
through natural selection of structures, which it is thought would be
beneficial to certain species. One writer asks, why has not the
ostrich acquired the power of flight ? But a moment's reflection
will show what an enormous supply of food would be necessary to
give to this bird of the desert force to move its huge body through
the air. Oceanic islands are inhabited by bats and seals, but by no
terrestrial mammals ; yet as some of these bats are peculiar species,
they must have long inhabited their present homes. Therefore
Sir C. Lyell asks, and assigns certain reasons in answer, why have
not seals and bats given birth on such islands to forms fitted to
live on the land ? But seals would necessarily be first converted
into terrestrial carnivorous animals of considerable size, and bats into
terrestrial insectivorous animals ; for the former there would be
no prey ; for the bats ground-insects would serve as food, but
these would already be largely preyed on by the reptiles or birds,
which first colonise and abound on most oceanic islands. Gradations
of structure, with each stage beneficial to a changing species, will
be favoured only under certain peculiar conditions. A strictly
terrestrial animal, by occasionally hunting for food in shallow
water, then in streams or lakes, might at last be converted into an
animal so thoroughly aquatic as to brave the open ocean. But seals
would not find on oceanic islands the conditions favourable to their
gradual reconversion into a terrestrial form. Bats, as formerly
shown, probably acquired their wings by at first gliding through
the air from tree to tree, like the so-called fiying-squirreLst

CHAP. VIL] THEORY OF NATURAL SELECTION. 181

for the sake of escaping from their enemies, or for aroiding falls ;
but when tho power of true flight had once been acquired, it would
never be reconverted back, at least for the above purposes, into the
kss efficient power of gliding through the air. Bats might, indeed,
like many birds, have had their wings greatly reduced in size, or
completely lost, through disuse; but in this case it would be
necessary that they should first have acquired the power of running
quickly on the ground, by the aid of their hind legs alone, so as to
compete with birds or other ground animals; and for such a change
a bat seems singularly ill-fitted. These conjectural remarks have
been made merely to show that a transition of structure, with each
step beneficial, is a highly complex affair ; and that there is nothing
strange in a transition not having occurred in any particular case.

Lastly, more than one writer has asked, why have some animals
had their mental povf er? more highly developed than others, as such
development would be advantageous to all? Why have not apes
acquired the intellectual powers of man ? Various causes could be
assigned ; but as they are conjectural, and their relative probability
cannot be weighed, it would be useless to give them. A definite
answer to the latter question ought not to be expected, seeing that
no one can solve the simpler problem why, of two races of savages,
one has risen higher in the scale of civilisation than the other ; and
this apparently implies increased brain-power.

We will return to Mr. Mivart's other objections. Insects often
resemble for the sake of protection various objects, such as green or
decayed leaves, dead twigs, bits of lichen, flowers, spines, excrement
of birds, and living insects ; but to this latter point I shall here-
after recur. The resemblance is often wonderfully close, and is not
confined to colour, but extends to form, and even to the manner in
which the insects hold themselves. The caterpillars which project
motionless like dead twigs from the bushes on which they feed,
offer an excellent instance of a resemblance of this kind. The
cases of the imitation of such objects as the excrement of birds, are
rare and exceptional. On this head, Mr. Mivart remarks, "As,
according to Mr. Darwin's theory, there is a constant tendency to
indefinite variation, and as the minute incipient variations will be
in all directions, they must tend to neutralize each other, and at
first to form such unstable modifications that it is difficult, if not
impossible, to see how such indefinite oscillations of infinitesimal
beginnings can ever build up a sufficiently appreciable resemblance
to a leaf, bamboo, or other object, for Natural Seliction to seize
upon and perpetuate."

182 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII.

But in all the foregoing cases the insects in their original state
no doubt presented some rude and accidental resemblance to an
object commonly found in the stations frequented by them. Nor
is this at all improbable, considering the almost infinite number of
surrounding objects and the diversity in form and colour of the
hosts of insects which exist. As some rude resemblance is neces-
sary for the first start, we can understand how it is that the larger
and higher animals do not (with the exception, as far as I know, of
one fish) resemble for the sake of protection special objects, but
only the surface which commonly surrounds them, and this chiefly
in colour. Assuming that an insect originally happened to resemble
in some degree a dead twig or a decayed leaf, and that it varied
slightly in many ways, then all the variations which rendered the
insect at all more like any such object, and thus favoured its escape,
would be preserved, whilst other variations would be neglected and
ultimately lost ; or, if they rendered the insect at all less like the
imitated object, they would be eliminated. There would indeed be
force in Mr. Mivart's objection, if we were to attempt to account
for the above resemblances, independently of natural selection,
through mere fluctuating variability ; but as the case stands there
is none.

Nor can I see any force in Mr. Mivart's difficulty with respect to
" the last touches of perfection in the mimicry ;" as in the case
given by Mr. Wallace, of a walking-stick insect (Ceroxylus
iaceratus), which resembles "a stick grown over by a creeping
moss or jungermannia." So close was this resemblance, that a
native Dyak maintained that the foliaceous excrescences were really
moss. Insects are preyed on by birds and other enemies, whose
sight is probably sharper than ours, and every grade in resemblance
which aided an insect to escape notice or detection, would tend
towards its preservation ; and the more perfect the resemblance so
much the better for the insect. Considering the nature of the differ-
ences between the species in the group which includes the above
Ceroxylus, there is nothing improbable in this insect having varied
in the irregularities on its surface, and in these having become more
or less green-coloured ; for in every group the characters which
differ in the several species are the most apt to vary, whilst the
generic characters, or those common to all the species, are the most
constant.

The Greenland whale is one of the most wonderful animals in the
world, and the baleen, or whale-bone, one of its greatest pecu-
liarities. The baleen consists of a row, on each side, of the upper

Chap. VII.] THEORY OF NATURAL SELECTION. 183

jaw, of about 300 plates or laminse, which stand close together
transversely to the longer axis of the mouth. Within the main row
there are some subsidiary rows. The extremities and inner margins
of all the plates are frayed into stiff bristles, which clothe the whole
gigantic palate, and serve to strain or sift the water, and thus to
secure the minute prey on which these great animals subsist. The
middle and longest lamina in the Greenland whale is ten, twelve, or
even fifteen feet in length ; but in the different species of Cetaceans
there are gradations in length; the middle lamina being in one
species, according to Scoresby, four feet, in another three, in
another eighteen inches, and in the Balsenoptera rostrata only about
nine inches in length. The quality of the whale-bone also differs in
the different species.

With respect to the baleen, Mr. Mivart remarks that if it " had
once attained such a size and development as to be at all useful,
then its preservation and augmentation within serviceable limits
would be promoted by natural selection alone. But how to obtain
the beginning of such useful development ? " In answer, it may
be asked, why should not the early progenitors of the whales with,
baleen have possessed a mouth constructed something like the
lamellated beak of a duck ? Ducks, like whales, subsist by sifting
the mud and water; and the family has sometimes been called
CrihlatoreSj or sifters. I hope that I may not be misconstrued inta
saying that the progenitors of whales did actually possess mouths
lamellated like the beak of a duck. I wish only to show that this
is not incredible, and that the immense plates of baleen in the
Greenland whale might have been developed from such lamellae by
finely graduated steps, each of service to its possessor.

The beak of a shoveller-duck (Spatula clypeata) is a more beau-
tiful and complex structure than the mouth of a whale. The upper
mandible is furnished on each side (in the specimen examined by
me) with a row or comb formed of 188 thin, elastic lamellse,
obliquely bevelled so as to be pointed, and placed transversely to
the longer axis of the mouth. They arise from the palate, and are
attached by flexible membrane to the sides of the mandible. Those
standing towards the middle are the longest, being about one-third
of an inch in length, and they project * 14 of an inch beneath the
edge. At their bases there is a short subsidiary row of obliquely
transverse lamellae. In these several respects they resemble the
plates of baleen in the mouth of a whale. But towards the
extremity of the beak they differ much, as they project inwards,
instead of straight downwards. The entire head of the shoveller,
though incomparably less bulky, is about one-eighteenth of the

1 84 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII

lerLgth of the heaxi of a moderately large Balasnoptera rostrata, in
which species the baleen is only nine inches long ; so that if we
were to make the head of the shoveller as long as that of the
Baleenoptera, the lamellas would be six inches in length, — that is,
two-thirds of the length of the baleen in this species of whale. The
lower mandible of the shoveller-dnck is furnished with lamellae of
equal length with those above, but finer ; and in being thus fur-
nished it differs conspicuously from the lower jaw of a whale, which
is destitute of baleen. On the other hand, the extremities of these
lower lamellse are frayed into fine bristly points, so that they thus
curiously resemble the plates of baleen. In the genus Prion, a
member of the distinct family of the Petrels, the upper mandible
alone is furnished with lamellge, which are well developed and
project beneath the margin ; so that the beak of this bird resembles
in this respect the mouth of a whale.

From the highly developed structure of the shoveller's beak we
may proceed (as I have learnt from information and specimens sent
to me by Mr. Salvin), without any great break, as far as fitness for
sifting is concerned, through the beak of the Merganetta armata, and
in some respects through that of the Aix sponsa, to the beak of the
common duck. In this latter species, the lamellse are much coarser
than in the shoveller, and are firmly attached to the sides of the
mandible ; they are only about 50 in number on each side, and do not
project at all beneath the margin. They are square-topped, and aro
edged with translucent hardish tissue, as if for crushing food. The
edges of the lower mandible are crossed by numerous fine ridges,
which project very little. Although the beak is thus very inferior
as a sifter to that of the shoveller, yet this bird, as every one knows,
constantly uses it for this purpose. There are other species, as I
hear from Mr. Salvin, in which the lamellae are considerably less
developed than in the common duck ; but I do not know whether
they use their beaks for sifting the water.

Turning to another group of the same family. In the Egyptian
goose (Chenalopex) the beak closely resembles that of the common
duck ; but the lamellaB are not so numerous, nor so distinct from
each other, nor do they project so much inwards ; yet this goose, is
I am informed by Mr. E. Bartlett, " uses its bill like a duck by
throwing the water out at the corners." Its chief food, howeA-er, is
grass, which it crops like the common goose. In this latter bird^
the lamella3 of the upper mandible are much coarser than in the
common duck, almost confluent, about 27 in number on each
side, and terminating upwards in teeth-like knobs. The palate is
also covered with hard rounded knobs. The edges of the lower

Chap. VII.] THEORY OF NATURAL SELECTION. 185

mandible are serrated with teeth much more prominent, coarser,
and sharper than in the duck. The common goose does not sift the
water, but uses its beak exclusively for tearing or cutting herbage,
for which purpose it is so well fitted, that it can crop grass closer
than almost any other animal. There are other species of geese, as
I hea;r from Mr. Bartlett, in which the lamellas are less developed
than in the common goose.

We thus see that a member of the duck family, with a beak
constructed like that of the common goose and adapted solely for
grazing, or even a member with a beak having less well-developed
lamellae, might be converted by small changes into a species like
the Egyptian goose, — this into one like the common duck, — and,
lastly, into one like the shoveller, provided with a beak almost
exclusively adapted for sifting the water ; for this bird could hardly
use any part of its beak, except the hooked tip, for seizing or tearing
solid food. The beak of a goose, as I may add, might also be con-
verted by small changes into one provided with prominent, recurved
teeth, like those of the Merganser (a member of the same family),
serving for the widely different purpose of securing live fish.

Eeturning to the whales. The Hyperoodon bidens is destitute of
true teeth in an efficient condition, but its palate is roughened,
according to Lacepede, with small, unequal, hard points of horn.
There is, therefore, nothing improbable in supposing that some
early Cetacean form was provided with similar points of horn on the
palate, but rather more regularly placed, and which, like the knobs
on the beak of the goose, aided it in seizing or tearing its food. If
so, it will hardly be denied that the points might have been con-
verted through variation and natural selection into lamellae as well-
developed as those of the Egyptian goose, in which case they would
have been used both for seizing objects and for sifting the water ;
then into lamellae like those of the domestic duck ; and so onwards,
until they became as well constructed as those of the shoveller, in
which case they would have served exclusively as a sifting appa-
ratus. From this stage, in which the lamellae would be two-thirds
of the length of the plates of baleen in the Balaenoptera rostrata,
gradations, which may be observed in still-existing Cetaceans, lead
us onwards to the enormous plates of baleen in the Greenland
whale. Nor is there the least reason to doubt that each step in
this scale might have been as serviceable to certain ancient Ceta-
ceans, v;ith the functions of the parts slowly changing during the
progress of development, as are the gradations in the beaks oi
the differ3nt existing members of the duck-family. We should
bear in mind that each species of duck is subjected to a severe

1 86 MISOFXLANEOUS OBJECTIONS TO THE [Chap. VII,

struggle for existence, and that the structure of every part of its
frame must be well adapted to its conditions of life.

The Pleuronectidse, or Flat-fish, are remarkable for their asym-
metrical bodies. They rest on one side, — in the greater number of
species on the left, but in some on the right side ; and occasionallj
reversed adult specimens occur. The lower, or resting-surface, re-
sembles at first sight the ventral surface of an ordinary fish : it is of
a white colour, less developed in many ways than the upper side,
with the lateral fins often of smaller size. But the eyes offer the
most remarkable peculiarity ; for they are both placed on the upper
side of the head. During early youth, however, they stand oppo-
site to each other, and the whole body is then symmetrical, with
both sides equally coloured. Soon the eye proper to the lower side
begins to glide slowly round the head to the upper side ; but does
not pass right through the skull, as was formerly thought to be
the case. It is obvious that unless the lower eye did thus travel
round, it could not be used by the fish whilst lying in its habitual
position on ono side. The lower eye would, also, have been liable
to be abraded by the sandy bottom. That the Pleuronectidse are
admirably adapted by their flattened and asymmetrical structure
for their habits of life, is manifest from several species, such as
soles, flounders, &c., being extremely common. The chief ad-
vantages thus gained seem to be protection from their enemies,
and facility for feeding on the ground. The difi"erent members,
however, of the family present, as Schiodte remarks, " a long series
of forms exhibiting a gradual transition from Hippoglossus pinguis,
which does not in any considerable degree alter the shape in which
it leaves the ovum, to the soles, which are entirely thrown to one
side.*'

Mr. Mivart has taken up this case, and remarks that a sudden
spontaneous transformation in the position of the eyes is hardly
conceivable, in which I quite agree with him. He then adds : " if
the transit was gradual, then how such transit of one eye a minute
traction of the journey towards the other side of the head could
benefit the individual is, indeed, far from clear. It seems, even,
that such an incipient transformation must rather have been inju-
rious." But he might have found an answer to this objection in
the excellent observations published in 1867 by Malm. The
Pleuronectida3, whilst very young; and still symmetrical, with their
eyes standing on opposite sides of the head, cannot long retain
a vertical position, owing to the excessive depth of their bodies, the
small Bize of their lateral fins, and to their being destitute of a

Chap. VII.] THEORY OF NATURAL SELECTION. 187

swimbladder. Hence soon growing tired, they fall to the bottom
on one side. Whilst thus at rest they often twist, as Malm
observed, the lower eye upwards, to see above them ; and they
do this so vigorously that the eye is pressed hard against the
upper part of the orbit. The forehead between the eyes conse-
quently becomes, as could be plainly seen, temporarily contracted
in breadth. On one occasion Malm saw a young fish raise and
depress the lower eye through an angular distance of about seventy
degrees.

AYe should remember that the skull at this early age is cartila-
ginous and flexible, so that it readily yields to muscular action.
It is also known with the higher animals, even after early youth,
that the skull yields and is altered in shape, if the skin or muscles
be permanently contracted through disease or some accident. With
long-eared rabbits, if one ear lops forwards and downwards, its
weight drags forward all the bones of the skull on the same side, of
which I have given a figure. Malm states that the newly-hatched
young of perches, salmon, and several other symmetrical fishes,
have the habit of occasionally resting on one side at the bottom ;
and he has observed that they often then strain their lower eyes
so as to look upwards ; and their skulls are thus rendered rather
crooked. These fishes, however, are soon able to hold themselves
in a vertical position, and no permanent effect is thus produced.
With the Pleuronectidse, on the other hand, the older they grow
the more habitually they rest on one side, owing to the increasing
flatness of their bodies, and a permanent efi"ect is thus produced on
the form of the head, and on the position of the eyes. Judging
ffom analogy, the tendency to distortion would no doubt be
increased through the principle of inheritance. Schiodte believes,
in opposition to some other naturalists, that the Pleuronectidje are
not quite symmetrical even in the embryo ; and if this be so, we
could understand how it is that certain species, whilst young,
habitually fall over and rest on the left side, and other species on
the right side. Malm adds, in confirmation of the above view, that
the adult Trachypterus arcticus, which is not a member of the
Pleuronectidse, rests on its left side at the bottom, and swims
diagonally through the water ; and in this fish, the two sides of the
head are said to be somewhat dissimilar. Our great authority on
Fishes, Dr. Giinther, concludes his abstract of Malm's paper, by
remarking that " the author gives a very simple explanation of the
abnormal condition of the Pleuronectoids."

We thus see that the first stages of the transit of the eyo from
gho cide of the head to the other, which Mr. Mivart considers woiild

188 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII-

be injurious, may be attributed to the habit, no doubt bene-
ficial to the individual and to the species, of endeavouring to
look upwards with both eyes, whilst resting on one side at the
bottom. We may also attribute to the inherited effects of use
the fact of the mouth in several kinds of flat-fish being bent
towards the lower surface, with the jaw bones stronger and more
effective on this, the eyeless side of the head, than on the other,
for the sake, as Dr. Traquair supposes, of feeding with ease on the
ground. Disuse, on the other hand, will account for the less deve-
loped condition of the whole inferior half of the body, including the
lateral fins ; though Yarrell thinks that the reduced size of these
fins is advantageous to the fish, as " there is so much less room for
their action, than with the larger fins above." Perhaps the lesser
number of teeth in the proportion of four to seven in the upper
halves of the two jaws of the plaice, to twenty-five to thirty in the
lower halves, may likewise be accounted for by disuse. From the
colourless state of the ventral surface of most fishes and of many
other animals, w^e may reasonably suppose that the absence of
colour in flat-fish on the side, whether it be the right or left,
which is undermost, is due to the exclusion of light. But it can-
not be supposed that the peculiar speckled appearance of the upper
side of the sole, so like the sandy bed of the sea, or the power in
some species, as recently shown by Pouchet, of changing their
colour in accordance with the surrounding surface, or the presence
of bony tubercles on the upper side of the turbot, are due to the
action of the light. Here natural selection has probably come into
play, as well as in adapting the general shape of the body of these
fishes, and many other peculiarities, to their habits of life. We
should keep in mind, as I have before insisted, that the inherited
effects of the increased use of parts, and perhaps of their disuse, will
be strengthened by natural selection. For all spontaneous varia-
tions in the right direction will thus be preserved ; as will those
individuals which inherit in the highest degree the effects of the
increased and beneficial use of any part. How much to attribute in
each particular case to the effects of use, and how much to natural
selection, it seems impossible to decide.

I may give auDther instance of a structure which apparently owes
its origin exclusively to use or habit. The extremity of the tail in
some American monkeys has been converted into a wonderfully
perfect prehensile organ, and serves as a fifth hand. A reviewer
who agrees with Mr. Mivart in every detail, remarks on this struc-
ture : " It is impossible to believe that in any number of ages the
first slight incipient tendency to grasp could preserve the lives of

Chap. VII.] THEORY OF NATURAL SELECTION. 189

the individuals possessing it, or favour their chance of having and
of rearing offspring." But there is no necessity for any such belief.
Habit, and this almost implies that some benefit great or small is
thus derived, would in all probability suffice for the work. Brehm
saw the young of an African monkey (Cercopithecus) clinging to
the under surface of their mother by their hands, and at the same
lime they hooked their little tails round that of their mother.
Professor Henslow kept in confinement some harvest mice (Mua
messorius) which do not possess a structurally prehensile tail ; but
he frequently observed that they curled their tails round the
branches of a bush placed in the cage, and thus aided themselves
in cHmbing. I have received an analogous account from Dr.
Giinther, who has seen a mouse thus suspend itself. If the harvest
mouse had been more strictly arboreal, it would perhaps have had
its tail rendered structurally prehensile, as is the case with some
members of the same order. Why Cercopithecus, considering its
habits whilst young, has not become thus provided, it would be
difficult to say. It is, however, possible that the long tail of this
monkey may be of more service to it as a balancing organ in
making its prodigious leaps, than as a prehensile organ.

The mammary glands are common to the whole class of mam-
mals, and are indispensable for their existence ; they must, there-
fore, have been developed at an extremely remote period, and we
can know nothing positively about their manner of development.
Mr. Mivart asks : " Is it conceivable that the young of any animal
was ever saved from destruction by accidentally sucking a drop of
scarcely nutritious fluid from an accidentally hypertrophied cuta-
neous gland of its mother ? And even if one was so, what chance
was there of the perpetuation of such a variation ? " But the case
is not here put fairly. It is admitted by most evolutionists that
mammals are descended from a marsupial form ; and if so, the
mammary glands will have been at first developed within the mar-
supial sack. In the case of the fish (Hippocampus) the eggs are
hatched, and the young are reared for a time, within a sack of thia
nature ; and an American naturalist, Mr. Lockwood, believes from
what he has seen of the development of the young, that they are
nourished by a secretion from the cutaneous glands of the sack.
Now with the early progenitors of mammals, almost before they
deserved to be thus designated, is it not at least possible that the
young might have been similarly nourished ? And in this case,
the individuals which secreted a fluid, in some degree or manner
the most nutritious, so as to partake of the nature of milk, would

190 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII.

in the long run have reared a larger numher cf well-nourished off-
spring, than would the individuals which secreted a poorer fluid ;
and thus the cutaneous glands, which are the homologues of the
mammary glands, would have been improved or rendered more
effective. It accords with the widely extended principle of speciali-
sation, that the glands over a certain space of the sack should have
become more highly developed than the remainder ; and they would
then have formed a breast, but at first without a nipple, as we see in
the Ornithorhyncus, at the base of the mammalian series. Through
what agency the glands over a certain space became more highly
specialised than the others, I will not pretend to decide, whether
in part through compensation of growth, the effects of use, or of
natural selection.

The development of the mammary glands would have been of no
service, and could not have been effected through natural selection,
unless the young at the same time were able to partake of the
secretion. There is no greater difficulty in understanding how
young mammals have instinctively learnt to suck the breast, than
in understanding how unhatched chickens have learnt to break the
egg-shell by tapping against it with their specially adapted beaks ;
or how a few hours after leaving the shell they have learnt to pick
up grains of food. In such cases the most probable solution seems
to be, that the habit was at first acquired by practice at a more
advanced age, and afterwards transmitted to the offspring at an
earlier age. But the young kangaroo is said not to suck, only to
cling to the nipple of its mother, who has the power of injecting
milk into the mouth of her helpless, half-formed offspring. On this
head Mr. Mivart remarks : " Did no special provision exist, the
young one must infallibly be choked by the intrusion of the milk
into the windpipe. But there is a special provision. The larynx
is so elongated that it rises up into the posterior end of the nasal
passage, and is thus enabled to give free entrance to the air for the
lungs, while the milk passes harmlessly on each side of this elon-
gated larynx, and so safely attains the gullet behind it." Mr. Mivart
then asks how did natural selection remove in the adult kangaroo
(and in most other mammals, on the assumption that they are
descended from a marsupial form), " this at least perfectly innocent
and harmless structure ? " It may be suggested in answer that the
voice, which is certainly of high importance to many animals, could
hardly have been used with full force as long as the larynx entered
the nasal passage ; and Professor Flower has suggested to me that
this structure would have greatly interfered with an animal swallow-
ing; solid food.

:hap. VJI.] THEORr OF NATURAL SELECTION. 191

We will now turn for a short space to the lower divisions of tiie
animal kingdom. The Echinodermata (star-fishes, sea-urchins, &c.)
are furnished with remarkable organs, called pediccllaria3, which
consist, when well developed, of a tridactyle forceps — that is, of one
formed of three serrated arms, neatly fitting together and placed on
the summit of a flexible stem, moved by muscles. These forceps
can seize firmly hold of any object ; and Alexander Agassiz has
seen an Echinus or sea-urchin rapidly passing particles of excrement
from forceps to forceps down certain lines of its body, in order that
its shell should not be fouled. But there is no doubt that besides
removing dirt of all kinds, they subserve other functions ; and one
of these apparently is defence.

With respect to these organs, Mr. Mivart, as on so many pre-
vious occasions, asks : " What would be the utility of the first
rudimentary heginnings of such structures, and how could such
incipient buddings have ever preserved the life of a single Echinus ? ''
He adds, " not even the sudden development of the snapping action
could have been beneficial without the freely moveable stalk, nor
could the latter have been efficient without the snapping jaws, yet
no minute merely indefinite variations could simultaneously evolve
these complex co-ordinations of structure ; to deny this seems to do
no less than to af&rm a startling paradox." Paradoxical as this
may appear to Mr. Mivart, tridactyle forcepses, immovably fixed
at the base, but capable of a snapping action, certainly exist on
some star-fishes ; and this is intelligible if they serve, at least in
part, as a means of defence. Mr. Agassiz, to whose great kindness
I am indebted for much information on the subject, informs me
that there are other star-fishes, in which one of the three arms of
the forceps is reduced to a support for the other two ; and again,
other genera in which the third arm is completely lost. In Echino-
neus, the shell is described by M. Perrier as bearing two kinds of
pedicellarias, one resembling those of Echinus, and the other those
of Spatangus; and such cases are always interesting as affording
the .means of apparently sudden transitions, through the abortion of
one of the two states of an organ.

With respect to the steps by which these curious organs have
been evolved, Mr. Agassiz infers from his own researches and those
of Miiller, that both in star-fishes and sea-urchins the pedicellarise
must imdoubtedly be looked at as modified spines. This may be
inferred from their manner of development in the individual, as
well as from a long and perfect series of gradations in different
species and genera, from simple granules to ordinary spines, to
perfect tridactyle pedi4}ellari£e. The gradation extends evei ir

192 MISCELLANEOUS OBJECTIONS TO THE [Chap. \.

the manner in which ordinary spines and the pedicellariaa with
their supporting calcareous rods are articulated to the shell. Li
certain genera of star-fishes, "the very combinations needed to
show that the pedicellaria3 are only modified branching spines"
may be found. Thus we have fixed spines, with three equi-distant,
serrated, moveable branches, articulated to near their bases ; and
higher up, on the same spine, three other moveable branches.
Xow when the latter arise from the summit of a spine they form
in fact a rude tridactyle pedicellaria, and such may be seen on the
same spine together with the three lower branches. In this case
the identity in nature between the arms of the pedicellarise and the
moveable branches of a spine, is unmistakeable. It is generally
admitted that the ordinary spines serve as a protection ; and if so,
there can be no reason to doubt that those furnished with serrated
and moveable branches likewise serve for the same purpose ; and
they would thus serve still more effectively as soon as by meeting
together they acted as a prehensile or snapping apparatus. Thus
every gradation, from an ordinary fixed spine to a fixed pedicellaria,
would be of service.

In certain genera of star-fishes these organs, instead of being
fixed or borne on an immovable support, are placed on the summit
of a flexible and muscular, though short, stem ; and in this case
they probably subserve some additional function besides defence.
In the sea-urchins the steps can be followed by which a fixed spine
becomes articulated to the shell, and is thus rendered moveable.
I wish I had space here to give a fuller abstract of Mr. Agassiz's
interesting observations on the development of the pedicellarias.
All possible gradations, as he adds, may likewise be found between
the pedicellarias of the star-fishes and the hooks of the Ophiuriaus,
another group of the Echinodermata ; and again between the pedi-
cellarise of sea-urchins and the anchors of the Holothurias, also
belonging to the same great class.

Certain compound animals, or zoophytes as they have been
termed, namely the Polyzoa, are provided with curious organs
called avicularia. These difi'er much in structure in the different
species. In their most perfect condition, they curiously resemble the
head and beak of a vulture in miniature, seated on a neck and cap-
able of movement, as is likewise the lower jaw or mandible. In one
species observed by me all the avicularia on the same branch often
moved simultaneously backwards and foi^ards, with the lower
jaw widely open, through an angle of about 90°. in the course of
five seconds; and then movement caused the whole polyzoary to

Chap. VII.] THEORY OF NATURAL SELECTION. 193

tremble. When the jaws are touched with a needle they seize it
m) firmly that the branch can thus be shaken.

Mr. Mivart adduces this case, chiefly on account of the supposed
difficulty of organs, namely the avicularia of the Polyzoa and the
pedicellarise of the Echinodermata, which he considers as " essen-
tially similar," having been developed through natural selection in
widely distinct divisions of the animal kingdom. But, as far as
structure is concerned, I can see no similarity between tridactyle
pedicellariae and avicularia. The latter resemble somewhat more
closely the chela3 or pincers of Crustaceans ; and Mr. Mivart might
have adduced with equal appropriateness this resemblance as a
special difficulty ; or even their resemblance to the head and beak
of a bird. U'he avicularia are believed by Mr. Busk, Dr. Smitt, and
Dr. Nitsche — naturalists who have carefully studied this group — to
be homologous with the zooids and their cells which compose the
zoophyte ; the moveable lip or lid of the cell corresponding with the
lower and moveable mandible of the avicularium. Mr, Busk, how-
ever, does not know of any gradations now existing between a zooid
and an avicularium. It is therefore impossible to conjecture by
what serviceable gradations the one could have been converted into
the other : but it by no means follows from this that such grada-
tions have not existed.

As the chelse of Crustaceans resemble in some degree the avicu-
laria of Polyzoa, both serving as pincers, it may be worth while to
show that with the former a long series of serviceable gradations
still exists. In the first and simplest stage, the terminal segment
of z. limb shuts down either on the square summit of the broad
penultimate segment, or against one whole side ; and is thus enabled
to catch hold of an object ; but the limb still serves as an organ
of locomotion. We next find one corner of the broad penultimate
segment slightly prominent, sometimes furnished with irregular
teeth ; and against these the terminal segment shuts down. By an
increase in the size of this projection, with its shape, as well as that
of the terminal segment, slightly modified and improved, the pincers
are rendered more and more perfect, until we have at last an instru-
ment as efficient as the chela) of a lobster ; and all these gradations
can be actually traced.

Besides the avicularia, the Polyzoa possess curious organs called
viljacula. These generally consist of long bristles, capable of
movement and easily excited. In one species examined by me
the vibracula were slightly curved and serrated along the outer
margin ; and all of them on the same polyzoary often moved simul-
taneously ; so that, acting like long oars, they swept a branch rapidly

o

'i ' ' <j

Staif r--' ^, . ^

194 MISCELLANEOUS OBJECTIONS TO THE [Chap. VD.

across the object-glass of my microscope. When a branch was
placed on its face, the vihracula became entangled, and they made
violent efforts to free themselves. They are supposed to serve as
a defence, and may be seen, as Mr. Busk remarks,* "to sweep
slowly and carefully over the surface of the polyzoary, removing
what might be noxious to the delicate inhabitants of the cells when
their tentacula are protruded." The avicularia, like the vibracula,
probably serve for defence, but they also catch and kill small living
animals, which it is believed are afterwards swept by the currents
within reach of the tentacula of the zooids. Some species are
provided with avicularia and vibracula ; some With avicularia alone,
and a few with vibracula alone.

It is not easy to imagine two objects more widely different in
appearance than a bristle or vibraculum, and an avicularium like
the head of a bird ; yet they are almost certainly homologous and
have been developed from the same common source, namely a zooid
with its cell. Hence we can understand how it is that these
organs graduate in some cases, as I am informed by Mr. Busk,
into each other. Thus with the avicularia of several species of
Lepralia, the moveable mandible is so much produced and is so like
a bristle, that the presence of the upper or fixed beak alone serves
to determine its avicularian nature. The vibracula may have been
directly developed from the lips of the cells, without having passed
through the avicularian stage ; but it seems more probable that
they have passed through this stage, as during the early stages of
the transformation, the other parts of the cell with the included
zooid could hardly have disappeared at once. In many cases the
vibracula have a grooved support at the base, which seems to repre-
sent the fixed beak ; though this support in some species is quite
absent. This view of the development of the vibracula, if trust-
worthy, is interesting ; for supposing that all the species provided
with avicularia had become extinct, no one with the most vivid
imagination would ever have thought that the vibracula had originall}''
existed as part of an organ, resembling a bird's head or an irregular
box or hood. It is interesting to see two such widely different
organs developed from a common origin ; and as the moveable lip
of the cell serves as a protection to the zooid, there is no difficulty
in believing that all tbe gradations, by which the lip became con-
verted first into the lower mandible of an avicularium and then
into an elongated bristle, likewise served as a protection in different
ways and under different circumstances.

lu the vegetable kingdom Mr. Mivart only alludes to t-wo cases,

Chap. VII.] THEORY OF NATQEAL SELECTION. 195

namely the stiiicture of the flowers of orchids, and the movements
of climbing plants. With respect to the former, he says, " the
explanation of their origin is deemed thoroughly unsatisfactory —
utterly insuflBcient to explain the incipient, infinitesimal beginnings
of structures which are of utility only when they are considerably
developed." As I have fully treated this subject in another work,
1 will here give only a few details on one alone of the most striking
peculiarities of the flowers of orchids, namely their pollinia. A
pollinium when highly developed consists of a mass of pollen-grains,
affixed to an elastic foot-stalk or caudicle, and this to a little mass
of extremely viscid matter. The pollinia are by this means trans-
ported by insects from one flower to the stigma of another. In
some orchids there is no caudicle to the pollen-masses, and the
grains are merely tied together by fine threads ; but as these are
not confined to orchids, they need not here be considered ; yet I
may mention that at the base of the orchidaceous series, in Cypri-
pedium, we can see how the threads were probably first developed.
In other orchids the threads cohere at one end of the pollen-masses ;
and this forms the first or nascent trace of a caudicle. That this
is the origin of the caudicle, even when of considerable length and
highly developed, we have good evidence in the aborted pollen-
grains which can sometimes be detected embedded within the
central and solid parts.

With respect to the second chief peculiarity, namely the little
mass of viscid matter attached to the end of the caudicle, a long
series of gradations can be specified, each of plain service to the
plant. In most flowers belonging to other orders the stigma se-
cretes a little viscid matter. Now in certain orchids similar viscid
matter is secreted, but in much larger quantities by one alone of
the three stigmas ; and this stigma, perhaps in consequence of the
copious secretion, is rendered sterile. When an insect visits a flower
of this kind, it rubs off some of the viscid matter an(i thus at the
same time drags away some of the pollen -grains. From this simple
condition, which differs but little from that of a multitude of
common flowers, there are endless gradations, — to species in which
the pollen-mass terminates in a very short, free caudicle, — to others
in which the caudicle becomes firmly attached to the viscid matter,
with the sterile stigma itself much modified. In this latter case
we have a pollinium in its most highly developed and perfect con-
dition. He who will carefully examine the flowers of ordiids for
himself will not deny the existence of the above series of gradations
— from a mass of pollen-grains merely tied together by threads,
with the stigma differing but little from that v^f .aiv ordinary flower,

0 2

196 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII.

to a highly complex poUinium, admirably adapted for transportaJ
by insects ; nor will he deny that all the gradations in the several
species are admirably adapted in relation to the general * structure
of each flower for its fertilisation by different insects. In this, and
in almost every other case, the enquiry may be pushed further
backwards ; and it may be asked how did the stigma of an ordinary
flower become viscid, but as we do not know the full history of any
one group of beings, it is as useless to ask, as it is hopeless to
attempt answering, such questions.

We will now turn to climbing plants. These can be arranged in
a long series, from those which simply twine round a support, to
those which I have called leaf-climbers, and to those provided with
tendrils. In these two latter classes the stems have generally, but
not always, lost the power of twining, though they retain the power
of revolving, which the tendrils likewise possess. The gradations
from leaf-climbers to tendril-bearers are wonderfully close, and
certain plants may be indifferently placed in either class. But in
ascending the series from simple twiners to leaf-climbers, an impor-
tant quality is added, namely sensitiveness to a touch, by which
means the foot-stalks of the leaves or flowers, or these modified
and converted into tendrils, are excited to bend round and clasp
the touching object. He who will read my memoir on these plants
will, I think, admit that all the many gradations in function and
structure between simple twiners and tendril-bearers are in each
case beneficial in a high degree to the species. For instance, it
is clearly a great advantage to a twining plant to become a leaf-
climber ; and it is probable that every twiner which possessed
leaves with long foot-stalks would have been developed into a leaf-
climber, if the foot-stalks had possessed in any slight degree the
requisite sensitiveness to a touch.

As twining is tlie simplest means of ascending a support, and
forms the basis of our series, it may naturally be asked how did
plants acquire this power in an incipient degree, afterwards to be
improved and increased through natural selection. The power of
twining depends, firstly, on the stems whilst young being extremely
flexible (but this is a character common to many plants which are
not climbers) ; and, secondly, on their continually bending to all
points of the compass, one after the other in succession, in the same
order. By this movement the stems are inclined to all sides, and
are made to move round and round. As soon as the lowei- part A
of a stem strikes against any object and is stopped, the upper part
still goes on bending and revolving, and thus necessarily twines
round and up the support. The revolving movement ;eases after

Chap VII.] THEORY OF NATURAL SELECTION. 197

the early growth of each shoot. As in many widely separated
families of plants, single species and single genera possess the powei
of revolving, and have thus become twiners, they must have
independently acquired it, and cannot have inherited it from a
common progenitor. Hence I was led to predict that some slight
tendency to a movement of this kind would be found to be far from
uncommon with plants which did not climb ; and that this had
afforded the basis for natural selection to work on and improve.
When I made this prediction, I knew of only one imperfect case,
namely of the young flower-peduncles of a Maurandia which
revolved slightly and irregularly, like the stems of twining plants,
but without making any use of this habit. Soon afterwards Fritz
MUller discovered that the young stems of an Alisma and of a
Linum, — plants which do not climb and are widely separated in
the natural system, — revolved plainly, though irregularly ; and he
states that he has reason to suspect that this occurs with some other
plants. These slight movements appear to be of no service to the
plants in question ; anyhow, they are not of the least use in the way
of climbing, w^hich is the point that concerns us. Nevertheless we can
see that if the stems of these plants had been flexible, and if under
the conditions to which they are exposed it had profited them to as-
cend to a height, then the habit of slightly and irregularly revolving
might have been increased and utilised through natural selection,
until they had become converted into well-developed twining species.
With respect to the sensitiveness of the foot-stalks of the leaves
and flowers, and of tendrils, nearly the same remarks are applicable
as in the case of the revolving movements of twining plants. As
a vast number of species, belonging to widely distinct groups, are
endowed with, this kind of sensitiveness, it ought to be found in a
nascent condition in many plants which have not become climbers.
This is the case : I observed that the young flower-peduncles of
the above Maurandia curved themselves a little towards the side
which was touched. Morren found in several species of Oxalis that
the leaves and their foot-stalks moved, especially after exposure
to a hot sun, when they were gently and repeatedly touched, :>r
when the plant was shaken. I repeated these observations on some
other species of Oxalis with the same result ; in some of them the
movement was distinct, but was best seen in the young leaves ; in
others it was extremely slight. It is a more important fact that
according to the high authority of Hofmeister, the young shoots and
leaves of all plants move after being shaken ; and with climbing
plants it is, as we know, only during the early stage? z( growth that
the foot-stalks and tendrils are sensitive.

198 MISCELLANEOUS OBJECTIONS TO THE [Chap. VIL

It is scarcely possible that the above slight movements, due to
a touch or shake, in the young aud growing organs of plants, can
be of any functional importance to them. But plants possess, in
obedience to various stimuli, powers of movement, which are of
manifest importance to them ; for instance, towards and more rarely
from the light, — in opposition to, and more rarely in the direction
of, the attraction of gravity. When the nerves and muscles of an
animal are excited by galvanism or by the absorption of strychnine,
the consequent movements may be called an incidental result, for
the nerves and muscles have not been rendered specially sensitive to
these stimuli. So with plants it appears that, from having the
power of movement in obedience to certain stimuli, they are excited
in an incidental manner by a touch, or by being shaken. Hence
there is no great difiiculty in admitting that in the case of leaf-
climbers and tendril-bearers, it is this tendency which has been
taken advantage of and increased through natural selection. It is,
however, probable, from reasons which I have assigned in my
memoir, that this will have occurred only with plants which had
already acquired the power of revolving, and had thus become
twiners.

I have already endeavoured to explain how plants became twiners,
namely, by the increase of a tendency to slight and irregular
revolving movements, which were at first of no use to them ; this
movement, as well as that due to a touch or shake, being the inci-
dental result of the power of moving, gained for other and bene-
ficial purposes. Whether, during the gradual development of
climbing plants, natural selection has been aided by the inherited
effects of use, 1 will not pretend to decide; but we know that
certain periodical movements, for instance the so-called sleep of
plants, are governed by habit.

I have now considered enough, perhaps more than enough, of the
cases, selected with care by a skilful naturalist, to prove that natural
selection is incompetent to account for the incipient stages of useful
structures; and I have shown, as I hope, that there is no great
difficulty on this head. A good opportunity has thus been afforded
for enlarging a little on gradations of structure, often associated
with changed functions, — an important subject, which was not
treated at sufficient length in the former editions of this work. I
will now briefly recapitulate the foregoing cases.

With the giraffe, the contmued preservation of the individuals ot
some extinct high-reaching ruminant, which had the longest necks,
legs, &c., and could browse a little above the average height, and

Chap. VII.] THEORY OF NATURAL SELECTION. 1 9i*

tlie continued destruction of those which could not browse so hicrh
would have sufficed for the production of this remarkable quad-
ruped ; but the prolonged use of all the parts together with inherit-
ance will have aided in an important manner in their co-ordination.
With the many insects which imitate various objects, there is no
improbability in the belief that an accidental resemblance to some
common object was in each case the foundation for the work of
natural selection, since perfected through the occasional preservation
of slight variations which made the resemblance at all closer ; and
this will have been carried on as long as the insect continued to
vary, and as long as a more and more perfect resemblance led to its
escape from sharp-sighted enemies. In certain species of whales
there is a tendency to the formation of irregular little points of horn
on the palate ; and it seems to be quite within the scope of natural
selection to preserve all favourable variations, until the points were
converted first into lamellated knobs or teeth, like these on the
"beak of a goose, — then into short lamellae, like those of the domestic
ducks, — and then into lamellse, as perfect as those of the shoveller-
duck, — and finally into the gigantic plates of baleen, as in the mouth
of the Greenland whale. In the family of the ducks, the lamellae
are first used as teeth, then partly as teeth and partly as a sifting
apparatus, and at last almost exclusively for this latter purpose.

With such structures as the above lamellae of horn or whale-
bone, habit or use can have done little or nothing, as far as we
can judge, towards their development. On the other hand, the
transportal of the lower eye of a flat-fish to the upper side of
the head, and the formation of a prehensile tail, may be attributed
almost wholly to continued use, together with inheritance. With
respect to the mammae of the higher animals, the most probable
conjecture is that primordially the cutaneous glands over the whole
surface of a marsupial sack secreted a nutritious fluid ; and that
these glands were improved in function through natural selection,
and concentrated into a confined area, in which case they would
have formed a mamma. There is no more difficulty in under-
standing how the branched spines of some ancient Echinoderm,
which served as a defence, became developed through natural selec-
tion into tridactyle pedicellari^e, than in understanding the develop-
ment of the pincers of crustaceans, through slight, serviceable modi-
fications in the ultimate and penultimate segments of a limb,
which was at first used solely for locomotion. In the avicularia
and vibracula of the Polyzoa we have organs w idely different in
appearance developed trom the same source ; and w ith the vibracula
y^ii can understand how the successive gradations might have been

200 MISCELLANEOUS OBJECTIONS TO THE [Chap. ^1

of service. With the pollinia of orchids, the threads which originally
served to tie together the pollen-grains, can be traced cohering into
caudicles ; and the steps can likewise be followed by which viscid
matter, such as that secreted by the stigmas of ordinary flowers, and
Btill subserving nearly but not quite the same purpose, became
attached to the free ends of the caudicles; — all these gradations
being of manifest benefit to the plants in question. With respect
to climbing plants, I need not repeat what has been so lately said.

It has often been asked, if natural selection be so potent, why has
not this or that structure been gained by certain species, to which it
would apparently have been advantageous ? But it is unreasonable to
expect a precise answer to such questions, considering our ignorance
of the past history of each species, and of the conditions which at
the present day determine its numbers and range. In most cases
only general reasons, but in some few cases special reasons, can be
assigned. Thus to adapt a species to new habits of life, many co-
ordinated modifications are almost indispensable, and it may often
have happened that the requisite parts did not vary in the right
manner or to the right degree. Many species must have been
prevented from increasing in numbers through destructive agencies,
which stood in no relation to certain structures, which we imagine
would have been gained through natural selection from appearing
to us advantageous to the species. In this case, as the struggle
for life did not depend on such structures, they could not have
been acquired through natural selection. In many cases complex
and long-enduring conditions, often of a peculiar nature, are neces-
sary for the development of a structure ; and the requisite con-
ditions may seldom have concurred. The belief that any given
structure, which we think, often erroneously, would have been
beneficial to a species, would have been gained under all circum-
stances through natural selection, is opposed to w^hat we can under-
stand of its manner of action. Mr. Mivart docs not deny that
natural selection has effected something ; but he considers it as
*' demonstrably insufficient " to account for the phenomena which I
explain by its agency. His chief arguments have now been con-
sidered, and the others will hereafter be considered. They seem to
me to partake little of the character of demonstration, and to have
little weight in comparison with those in favour of the power of
natural selection, aided by the other agencies often specified. I am
bound to add, that some of the facts and arguments here used by
me, have been advanced for the same purpose in an able article
lately published in the ' Medico-Chirurgical Review.'

Chap. VII.] THEORY OF NATURAL SELECTIONS 201

At the present day almost all naturalists admit evolution under
some form. Mr. Mivart believes that species change through "an
internal force or tendency," about which it is not pretended that
anything is known. That species have a capacity for change will
be admitted by all evolutionists ; but there is no need, as it seems
to me, to invoke any internal force beyond the tendency to ordi-
nary variability, "which through the aid of selection by man has
given rise to many well-adapted domestic races, and w^iich through
the aid of natural selection would equally well give rise by gradu-
ated steps to natural races or species. The final result will gene-
rally have been, as already explained, an advance, but in some few
cases a retrogression, in organisation.

Mr. Mivart is further inclined to believe, and soni-e naturalists
agree with him, that new species manifest themselves " with sud-
denness and by modifications appearing at once." For instance,
he supposes that the differences between the extinct three-toed
Hipparion and the horse arose suddenly. He thinks it difficult to
believe that the wing of a bird " was developed in any other way
than by a comparatively sudden mt)dification of a marked and
important kind ; " and apparently he would extend the same view-
to the wings of bats and pterodactyles. This conclusion, which
implies great breaks or discontinuity in the series, appears to me
improbable in the highest degree.

Every one who believes in slow and gradual evolution, will of
course admit that specific changes may have been as abrupt and as
great as any single variation which we meet with under nature,
or even under domestication. But as species are more variable
when domesticated or cultivated than under their natural con-
ditions, it is not probable that such great and abrupt variations
have often occurred under nature, as are known occasionally to
arise under domestication. Of these latter variations several may
be attributed to reversion ; and the characters which thus reappear
were, it is probable, in many cases at first gained in a gradual
manner. A still greater number must be called monstrosities, such
as six-fin.gered men, porcupine men, Ancon slieep, Niata cattle, &c. ;
and as they are widely different in character from natural species,
they throw very little light on our subject. Excluding such cases
of abrupt variations, the few which remain would at best constitute,
if found in a state of nature, doubtful species, closely related to
their parental types.

My reasons for doubting whether natural species have changed
as abruptly as have occasionally domestic races, and for entirely
disbelieving that they have changed in the wonderful mannej

202 MISCELLANEOUS OBJECTIONS TO THE [Chap. Vll

indicated by Mr. Mivart, are as follows. According to our expe-
rience, abrupt and strongly marked variations occur in our domesti-
cated productions, singly and at rather long intervals of time. If
such occurred under nature, they would be liable, as formerly
explained, to be lost by accidental causes of destruction and by
Bubsequent inter-crossing ; and so it is known to be under domesti-
cation, unless abrupt variations of this kind are specially preserved
and separated by the care of man. Hence in order that a new
species should suddenly appear in the manner supposed by Mr.
Mivart, it is almost necessary to believe, in opposition to all ana-
logy, that several wonderfully changed individuals appeared simul-
taneously within the same district. This difficulty, as in the case of
unconscious selection by man, is avoided on the theory of gradual
evolution, through the preservation of a large number of individuals,
which varied more or less in any favourable direction, and of the
destruction of a large number which varied in an opposite manner.

That many species have been evolved in an extremely gradual
manner, there can hardly be a doubt. The species and even the
genera of many large natural families are so closely allied together,
that it is difficult to distinguish not a few of them. On every con-
tinent in proceeding from north to south, from lowland to upland,
&c., we meet with a host of closely related or representative species ;
as we likewise do on certain distinct continents, which we have
reason to believe were formerly connected. But in making these
and the following remarks, I am compelled to allude to subjects
hereafter to be discussed. Look at the many outlying islands round
a continent, and see how many of their inhabitants can be raised
only to the rank of doubtful species. So it is if we look to past
times, and compare the species which have just passed away with
those still living within the same areas ; or if we compare the fossil
species embedded in the sub-stages of the same geological formation.
It is indeed manifest that multitudes of species are related in the
closest manner to other species that still exist, or have lately
existed ; and it will hardly be maintained that such s[iecies have
been developed in an abrupt or sudden manner. Nor should it be
forgotten, when we look to the special parts of allied species, instead
of to distinct species, that numerous and wonderfully fine grada-
tions can be traced, connecting together widely different structures.

Many large groups of facts are intelligible only on the principle
that species have been evolved by very small steps. For instance,
the fact that the species included in the larger genera are more closely
related to each other, and present a greater number of varieties
tha;' do the species in the smaller genera. The former are al»o

Chap. VII.] THEORY OF NATURAL SELECTION. 203

grouped in little clusters, like varieties round species; and they
present other analogies with varieties, as was shown in our second
chapter. On this same principle we can understand how it is that
specific characters are more variable than generic characters ; and
how the parts which are developed in an extraordinary degree
or manner are more variable than other parts of the same species.
Many analogous facts, all pointing in the same direction, could be
added.

Although very many species have almost certainly been pro-
duced by steps not greater than those separating fine varieties ; yet
It may be maintained that some have been developed in a different
and abrupt manner. Such an admission, however, ought not to be
made without strong evidence being assigned. The vague and in
some respects false analogies, as they have been shown to be by
Mr. Chauncey Wright, which have been advanced in favour of this
view, such as the sudden crystallisation of inorganic substances, or
the falling of a facetted spheroid from one facet to another, hardly
deserve consideration. One class of facts, however, namely, the
sudden appearance of new and distinct forms of life in our geological
formations supports at first sight the belief in abrupt development.
But the value of this evidence depends entirely on the perfection ol
the geological record, in relation to periods remote in the history
of the world. If the record is as fragmentary as many geologists
strenuously assert, there is nothing strange in new forms appear-
ing as if suddenly developed.

Unless we admit transformations as prodigious as those advocated
by Mr. Mivart, such as the sudden development of the wings of
birds or bats, or the sudden conversion of a Hipparion into a norse,
hardly any light is thrown by the belief in abrupt modifications on
the deficiency of connecting links in our geological formations. But
against the belief in such abrupt changes, embryology enters a strong
protest. It is notorious that the wings of birds and bats, and the legs
of horses or other quadrupeds, are undistinguishable at an early em-
bryonic period, and that they become ditlerentiated by insensibly
fine steps. Embryological resemblances of all kinds can be ac-
counted for, as we shall hereafter see, by the progenitors of our
existing species having varied after early youth, and having trans-
mitted their newly acquired characters to their offspring, at a
corresponding age. The embryo is thus left almost unaffected, and
serves as a record of the past condition of the species. Hence it
is that existing species during the early stages of their develop-
ment so often resemble ancient and extinct forms belonging to the
same class. On this view of the meaning of embryological rcsem-

204 MISCELLANEOUS OBJECTIONS, ETC. [Chap. VIl.

blances, and indeed on any view, it is incredible that an animal
should have undergone such momentous and abrupt transforma-
tions, as those above indicated ; and yet should not bear even a
trace in its embryonic condition of any sudden modification ; every
detail in its structure being developed by insensibly fine steps.

He who believes that some ancient form was transformed sud-
denly through an internal force or tendency into, for instance, one
furnished with wings, will be almost compelled to assume, in oppo-
"sition to all analogy, that many individuals varied simultaneously.
It cannot be denied that such abrupt and great changes of struc-
ture are widely different from those which most species apparently
have undergone. He will further be compelled to believe that
many structures beautifully adapted to all the other parts of the
same creature and to the surrounding conditions, have been sud-
denly produced ; and of such complex and wonderful co-adapta-
tions, he will not be able to assign a shadow of an explanation.
He will be forced to admit that these great and sudden transfor-
mations have left no trace of their action on the embryo. To
admit all this ib, as it seems to me, to enter into the realma of
mlKicle, and to leave those of Science.

Cbmv. VIII.] INSTINCT. 205

CHAPTER VIII.

Instinct.

Instincts comparable with habits, but different in their origin — Instincts
graduated — Aphides and ants — Instincts variable — Domestic ia
stincts, their origin — Natural instincts of the cuckoo, molothrus,
ostrich, and parasitic bees — Slave-making ants — Hive-bee, its cell-
making instinct — Changes of instinct and structure not necessarily
simultaneous — Difficulties of the theory of the Natural Selection of
instincts — Neuter or sterile insects — Summary.

Many instincts are so wonderful that their development will pro-
bably appear to the reader a difficulty sufficient to overthrow m^
whole theory. I may here premise, that I have nothing to do with
the origin of the mental powers, any more than I have with that of
life itself. We are concerned only with the diversities of instinct
and of the other mental faculties in animals of the same class.

I will not attempt any definition of instinct. It would be easy to . , ,
show that several distinct mental actions are commonly embraced Z^^-'"'^-'^
by this term ; but every one, understands what is meant, when it is ^
said that instinct impels the cuckoo to migrate and to lay her eggs
in other birds' nests. An action, which we ourselves require expe-
rience to enable us to perform, when performed by an animal, more
especially by a very young one, without experience, and when per-
formed by many individuals in the same way, without their knowing
for what purpose it is performed, is usually said to be instinctive.
But I could show that none of these characters are universal. A
little dose of judgment or reason, as Pierre Huber expresses it, oftep
comes into play, even with animals low in the scale of nature.

Frederick Cuvier and several of the older metaphysicians have
compared instinct with habit. This comparison gives, I think, an
accurate notion of the frame of mind under which an instinctive
action is performed, but not necessarily of its origin. How uncon-
sciously many habitual actions are performed, indeed not rarely in
direct opposition to our conscious will ! yet they may be modi-
fied by the will or reason. Habits easily become associated with
other habits, with certain periods of time, and states of the body.
When once acquired, they often remain constant throughout life.

200 INSTINCT. [Chap. VIII

Several other points of resemblance between instincts and habits
could be pointed out. As in repeating a well-known song, so in
instincts, one action follows another by a sort of rhythm ; if a person
be interrupted in a song, or in repeating anything by rote, he is
generally forced to go back to recover the habitual train of thought.
so P. Huber found it was with a caterpillar, which makes a very com-
plicated hanamock ; for if he took a caterpillar which had completed
its hammock up to, say, the sixth stage of construction, and put it
into a hammock completed up only to the third stage, the caterpillar
simply re-performed the fourth, fifth, and sixth stages of construction.
If, however, a caterpillar were taken out of a hammock made up,
for instance, to the third stage, and were put into one finished up to
the sixth stage, so that much of its work was already done for it,
far from deriving any benefit from this, it was much embarrassed,
and in order to complete its hammock, seemed forced to start from
the third stage, where it had left off, and thus tried to complete the
already finished work.

If we suppose any habitual action to become inherited — and it
can be shown that this does sometimes happen — then the resem-
blance between what originally was a habit and an instinct becomes
so close as not to be distinguished. If Mozart, instead of playing
the pianoforte at three years old with wonderfully little practice,
had played a tune with no practice at all, he might truly be said
to have done so instinctively. But it would be a serious error to
suppose that the greater number of instincts have been acquired by
habit in one generation, and then transmitted by inheritance to
succeeding generations. It can be clearly shown that the most
wonderful instincts with which we are acquainted, namely, those
of the hive-bee and of many ants, could not possibly have been
acquired by habit.

It will be universally admitted that instincts are as important as
corporeal structures for the welfare of each species, under its present
"conditions of life. Under changed conditions of life, it is at least
possible that slight modifications of instinct might be profitable to
a species ; and if it can be shown that instincts do vary ever so
little, then I can see no difiiculty in natural selection preservings
and continually accumulating variations of instinct to any extent
that was profitable. It is thus, as I believe, that all the most
complex and wonderful instincts have originated. As modifications
of corporeal structure arise from, and are increased by, use or habit,
and are diminished or lost by disuse, so I do not doubt it has been
with instincts. But I believe that the effects of habit are in many
ca.ses of subordinate importance to the effects of the natural selection

Chap. VIII.] LVSTINCT. 207

of wLat may he called ppontancons variations of instincts ; — that
is of variations produced by the same unknown causes which pro-
duce slight deviations of bodily structure.

No complex instinct can possibly be produced through natural
selection, except by the slow and gradual accumulation of numerous
slight, yet profitable, variations. Hence, as in the case of corporeal
structures, we ought to find in nature, not the actual transitional
gradations by which each complex instinct has been acquired — for
these could be found only in the lineal ancestors of each species —
but we ought to find in the collateral lines of descent some evidence
of such gradations ; or we ought at least to be able to show that
gradations of some kind are possible ; and this we certainly can do.
I have been surprised to find, making allowance for the instincts of
animals having been but little observed except in Europe and North
America, and for no instinct being known amongst extinct species,
how very generally gradations, leading to the most complex instincts,
can be discovered. Changes of instinct may sometimes be facilitated
by the same species having different instincts at different periods
of life, or at different seasons of the year, or when placed under
different circumstances, &c. ; in which case either the one or the
other instinct might be preserved by natural selection. And such
instances of diversity of instinct in the same species can be shown
to occur in nature.

Again, as in the case of corporeal structure, and conformably to
my theory, the instinct of each species is good for itself, but has
never, as far as we can judge, been produced for the exclusive good
of others. One of the strongest instances of an animal apparently
performing an action for the sole good of another, with which I am
acquainted, is that of aphides voluntarily yielding, as was first
observed by Iluber, their sweet excretion to ants : that they do so
voluntarily, the following facts show. I removed all the ants from
a group of about a dozen aphides on a dock-plant, and prevented
their attendance during several hours. After this interval, I felt
sure that the aphides would want to excrete. I watched them for
some time through a lens, but not one excreted ; I then tickled and
stroked them with a hair in the same manner, as well as I could,
as the ants do with their antennae ; but not one excreted. After-
wards I allowed an ant to visit them, and it immediately seemed,
by its eager v/ay of running about, to be well aware what a rich
flock it had discovered ; it then began to play with its antennae on
the abdomen first of one aphis and then of another ; and each, as
Boon as it felt the antennae, immediately lifted up its abdomen and
excreted a limpid drop of sweet juice, which was eagerly devoured

203 INSTINCT. [Chap. VIU.

by the ant. Even the quite young aphides lehavcd in this manner,
showing; that the action was instinctive, and not the result oi
experience. It is certain, from the observations of Huber, that the
aphides show no dislike to the ants : if the latter be not present
they are at last compelled to eject their excretion. But as the
excretion is extremely viscid, it is no doubt a convenience to the
aphides to have it removed ; therefore probably they do not excreta
solely for the good of the ants. Although there is no evidence that
any animal performs an action for the exclusive good of anothei
species, yet each tries to take advantage of the instincts of others,
as each takes advantage of the weaker bodily structure of other
species. So again certain instincts cannot be considered as abso-
lutely perfect ; but as details on this and other such points are not
indispensable, they may be here passed over.

As some degree of variation in instincts under a state of nature,
and the inheritance of such variations, are indispensable for the
action of natural selection, as many instances as possible ought to
be given ; but want of space prevents me. I can only assert that
instincts certainly do vary — for instance, the migratory instinct,
both in extent and direction, and in its total loss. So it is with the
nests of birds, which vary partly in dependence on the situations
chosen, and on the nature and temperature of the country inhabited,
but often from causes wholly unknown to us : Audubon has given
several remarkable cases of differences in the nests of the same
species in the northern and southern United States. Why, it has
been asked, if instinct be variable, has it not granted to the bee
" the ability to use some other material when wax was deficient " ?
But what other natural material could bees use ? They will work,
as I have seen, with wax hardened with vermilion or softened
with lard. Andrew Knigbt observed that his bees, instead of
laboriously collecting propolis, used a cement of wax and turpentine,
with which he had covered decorticated trees. It has lately been
shown that bees, instead of searching for pollen, will gladly use a
very different substance, namely oatmeal. Fear of any particular
enemy is certainly an instinctive quality, as may be seen in nestling
birds, though it is strengthened by experience, and by the sight of
fear of the same enemy in other animals. The fear of man is slowly
acquired, as I have elsewhere shown, by the various animals which
inhabit desert islands; and we see an instance of this even in
England, in the greater wildness of all our large birds in comparison
with our small birds ; for the large birds have been most persecuted
by man. We may safely attribute the greater wildness of our
large birds to this cause ; for in uninhabited islands large birds aiv

Chap. VIII.] CHANGES OF HABTT OR INSTINCT. 209

rot more fearful than small ; and the magpie, so wary in England,
is tame in Norway, as is the hooded crow in Egypt.

That the mental qualities of animals of the same kind, born in a
state of nature, vary much, could be shown by many facts. Several
cases could also be adduced of occasional and strange habits in
wild animals, which, if advantageous to the species, might have
given rise, through natural selection, to new instincts. But I am
well aware that these general statements, without the facts in
detail, will produce but a feeble effect on the reader's mind. I
can only repeat my assurance, that I do not speak without good
evidence.

Inherited Changes of Habit or Instinct in Domesticated

Animals.

The possibility, or even probability, of inherited variations of
instinct in a state of nature will be strengthened by briefly consider-
ing a few cases under domestication. We shall thus be enabled to
see the part which habit and the selection of so-called spontaneous
variations have played in modifying the mental qualities of our
domestic animals. It is notorious how much domestic animals vary
in their mental qualities. With cats, for instance, one naturally
takes to catching rats, and another mice, and these tendencies are
known to be inherited. One cat, according to Mr. St. John, always
brought home game-birds, another hares or rabbits, and another
hunted on marshy ground and almost nightly caught woodcocks or
snipes. A number of curious and authentic instances could be
given of various shades of disposition and of taste, and likewise of
the oddest tricks, associated with certain frames of mind or periods
of time, being inherited. But let us look to the familiar case of
the breeds of the dog : it cannot be doubted that young pointers (I
have myself seen a striking instance) will sometimes point and even
back other dogs the very first time that they are taken out ;
retrieving is certainly in some degree inherited by retrievers ; and a
tendency to run round, instead of at, a flock of sheep, by shepherd -
dogs. 1 cannot see that these actions, performed without experience
by the young, and in nearly the same manner by each individual,
performed with eager delight by each breed, and without the end '*^
being known — for the young pointer can no more know that he
points to aid his master, than the white butterfly knows why she
lays her eggs on the leaf of the cabbage — I cannot see that these
actions differ essentially from true instincts. If we were to benold
one kind of wolf, when young and without any training, as soon as
U scented its prey, stand motionless like a statue, and then slowly

p

210

CHANGES OF HABIT OR INSTINCT [Chap. VIII.

1

^;

crawl forward with a peculiar gait ; and another kind of wolf
rushing round, instead of at, a herd of deer, and driving them to a
distant point, we should assuredly call these actions instinctive.
Domestic instincts, as they may be called, are certainly far less
nxed than natural instincts ; but they have been acted on by far
less rigorous selection, and have been transmitted for an incompar-
ably shorter period, under less fixed conditions of life.

How strongly these domestic instincts, habits, and dispositions
are inherited, and how curiously they become mingled, is well
shown when different breeds of dogs are crossed. Thus it is known
that a cross with a bull-dog has affected for many generations the
courage and obstinacy of greyhounds ; and a cross with a greyhound
has given to a whole family of shepherd-dogs a tendency to hunt
hares. These domestic instincts, when thus tested by crossing,
resemble natural instincts, which in a like manner become curiously
blended together, and for a long period exhibit traces of the instincts
of either parent : for example, Le Eoy describes a dog, whose^eat-
grandfather was a wolf, and this dog showed a trace of its wdld
parentage only in one way, by not coming in a straight line to his
master, when called.

Domestic instincts are sometimes spoken of as actions which
have become inherited solely from long-continued and compulsory
habit ; but this is not true. No one would ever have thought of
teaching, or probably could have taught, the tumbler-pigeon to
tumble, — an action which, as I have witnessed, is performed by
young birds, that have never seen a pigeon tumble. We may
believe that some one pigeon showed a slight tendency to this
strange habit, and that the long-continued selection of the best
individuals in successive generations made tumblers what they now
are ; and near Glasgow there are house-tumblers, as I hear from
Mr. Brent, which cannot fly eighteen inches high without going
head over heels. It may be doubted whether any one would have
thought of training a dog to point, had not some one dog naturally
shown a tendency in this line ; and this is known occasionally to
happen, as I once saw, in a pure terrier : the act of pointing is pro-
bably, as many have thought, only the exaggerated pause of an
animal preparing to spring on its prey. When the first tendency
to point was once displayed, methodical selection and the inherited
efi'ects of compulsory training in each successive generation would
soon complete the work ; and unconscious selection is still in
progress, as each man tries to procure, without intending to improve
the breed, dogs which stand and hunt best. On the other hand,
habit alone in some cases has sufficed ; hardly any animal is more

Chap. VIII.] IN DOMESTICATED ANIMALS. 211

difficult to tame than the young of the wild rabbit ; scarcely any
animal is tamer than the young of the tame rabbit; but I can
hardly suppose that domestic rabbits have often been selected for
tameness alone ; so that we must attribute at least the greater part
of the inherited change from extreme wildness to extreme tame-
ness, to habit and long-continued close confinement.

Natural instincts are lost under domestication: a remarkable
instance of this is seen in those breeds of fowls which very rarely
or never become " broody," that is, never wish to sit on their eggs.
Familiarity alone prevents our seeing how largely and how perma-
nently the minds of our domestic animals have been modified. It
is scarcely possible to doubt that the love of man has become
instinctive in the dog. All wolves, foxes, jackals, and species of
the cat genus, when kept tame, are most eager to attack poultry,
sheep, and pigs; and this tendency has been found incurable in
dogs which have been brought home as puppies from countries such
as Tierra del Fuego and Australia, where the savages do not keep
these domestic animals. How rarely, on the other hand, do our
civilised dogs, even when quite young, require to be taught not to
attack poultry, sheep, and pigs ! No doubt they occasionally do
make an attack, and are then beaten ; and if not cured, they are
destroyed; so that habit and some degree of selection have pro-
bably concurred in civilising by inheritance our dogs. On the
other hand, young chickens have lost, wholly by habit, that fear of
the dog and cat which no doubt was originally instinctive in them ;
for I am informed by Captain Button that the young chickens of
the parent-stock, the Gallus bankiva, when reared in India under a
hen, are at first excessively wild. So it is with young pheasants
reared in England under a hen. It is not that chickens have lost
all fear, but fear only of dogs and cats, for if the hen gives the
danger-chuckle, they will run (more especially young turkeys) from
Tinder her, and conceal themselves in the surrounding grass or
thickets ; and this is evidently done for the instinctive purpose of
allowing, as we see in wild ground-birds, their mother to fly away.
But this instinct retained by our chickens has become useless under
domestication, for the mother-hen has almost lost by disuse the
power of flight.

Hence, we may conclude, that under domestication instincts have
been acquired, and natural instincts have been lost, partly by habit,
and partly by man selecting and accumulating, during successive
generations, peculiar mental habits and actions, which at first
appeared from what we must in our ignorance call an accident. In
some cases compulsory habit alone has sufficed to produce inhe-

p 2

212 SPECIAL INSTINCTS [Chap. VIIl.

rited mental changes; in other cases compulsory habit has done
nothing, and all has been the result of selection, pursued both
methodically and unconsciously: but in most cases habit and
eelection have probably concurred.

Special Instincts.

We shall, perhaps, best understand how instincts in a state of
nature have become modified by selection, by considering a few
cases. 1 will select only three,— namely, the instinct which leads
the cuckoo to lay her eggs in other birds' nests ; the slave-making
instinct of certain ants ; and the cell-making power of the
hive- bee. These two latter instincts have generally and justly
been ranked by naturalists as the most wonderful of all known
instincts.

Instincts of the CucTcoo. — It is supposed by some naturalists that
the more immediate cause of the instinct of the cuckoo is, that she
lays her eggs, not daily, but at intervals of two or three days ; so
that, if she were to make her own nest and sit on her own eggs,
those first laid would have to be left for some time unincubated, or
there would be eggs and young birds of different ages in the sama
nest. If this were the case, the process of laying and hatching
might be inconveniently long, more especially as she migrates at a
very early period ; and the first hatched young would probably
have to be fed by the male alone. But the American cuckoo is in
this predicament ; for she makes her own nest, and has eggs and
young successively hatched, all at the same time. It has been both
asserted and denied that the American cuckoo occasionally lays hei
eggs in other birds' nests ; but I have lately lieard from Dr. Merrell,
of Iowa, that he once found in Illinois a young cuckoo together
with a young jay in the nest of a Blue jay (Garrulus cristatus) ;
and as both were nearly fully feathered, there could be no mistake
in their identification. I could also give several instances of various
birds which have been known occasionally to lay their eggs in other
birds' nests. Kow let us suppose that the ancient progenitor of our
European cuckoo had the habits of the American cuckoo, and that
she occasionally laid an egg in another bird's nest. If the old bird
profited by this occasional habit through being enabled to migrate
earlier or through any other cause ; or if the young were made more
vigorous by advantage being taken of the mistaken instinct of
another species than when reared by their own mother, encum-
bered as she could hardly fail to be by having eggs and young of
different ages at the same time ; then the old birds or the fostered
ycung would gain an advantage. And analogy would lead us tc

Chap. VIII.] INSTINCTS OF THE CUCKOO. 213

believe, that the young thus reared would be apt to follow by inhe-
ritance the occasional and aberrant habit of their mother, and in
their turn would be apt to lay their eggs in other birds' nests, and
thus be more successful in rearing their young. By -a continued
process of this nature, I believe that the strange instinct of our
cuckoo has been generated. It has, also, recently been ascertained
on sufficient evidence, by Adolf Mliller, that the cuckoo occasionally
lays her eggs on the bare ground, sits on them, and feeds her young.
This rare event is probably a case of reversion to the long-lost,
aboriginal instinct of nidification.

It has been objected that I have not noticed ether related instincts
and adaptations of structure in the cuckoo, which are spoken of as
necessarily co-ordinated. But in all cases, speculation on an instinct
known to us only in a single species, is useless, for we have hitherto
had no facts to guide us. Until recently the instincts of the Euro-
pean and of the non-parasitic American cuckoo alone were known ;
now, owing to Mr. Eamsay's observations, we have learnt something
about three Australian species, which lay their eggs in other birds'
nests. The chief points to be referred to are three : first, that the
common cuckoo, with rare exceptions, lays only one egg in a nest,
so that the large and voracious young bird receives ample food,
Secondly, that the eggs are remarkably small, not exceeding those
of the skylark, — a bird about one-fourth as large as the cuckoo.
That the small size of the egg is a real case of adaptation we may
infer from the fact of the non-parasitic American cuckoo laying
full-sized eggs. Thirdly, that the young cuckoo, soon after birth,
has the instinct, the strength, and a properly shaped back for
<3iecting. i^sjoster-brothers, which then perish from cold and hunger.
This has been boldly called a beneficent arrangement, in order that
the young cuckoo may get sufficient ]oo3,^and that its foster-brothers
may pei-ish before J.liey had acquired much feeling!

Turning now to the Australian species ; though these birds gene-
rally lay only one egg in a nest, it is not rare to fi.nd two and even
three eggs in the same nest. In the Bronze cuckoo the eggs vary
greatly in size, from eight to ten lines in length. Now if it had
been of an advantage to this species to have laid eggs even smaller
than those now laid, so as to have deceived certain foster-parents,
or, as is more probable, to have been hatched within a shorter period
(for it is asserted that there is a relation between the size of eggs
and the period of their incubation), then there is no difficulty in
believing that a race or species might have been formed which
would have laid smaller and smaller eggs ; for these would have
been more safely hatched and reared. Mr. Kamsay remarks that

r^

•ft

-5

J

;i

\\\

^^ \>cj/^-i-

INSTINCT OF THE CUCKOO.

[Chap. VI 11.

two of the Australian cuckoos, when they lay their eggs in an open
nest, manifest a decided preference for nests containing eggs similar
in colour to their own. The European species apparently manifests
some tendency towards a similar instinct, but not rarely departs
from it, as is shown by her laying her dull and pale-coloured eggs
in the nest of the Hedge- warbler with bright greenish- blue eggs. Had
our cuckoo invariably displayed the above instinct, it would assu-
tedly have been added to those which it is assumed must all have
been acquired together. The eggs of the Australian Bronze cuckoo
vary, according to Mr. Ramsay, to an extraordinary degree in colour;
so that in this respect, as well as in size, natural selection might
have secured and fixed any advantageous variation.

In the case of the European cuckoo, the offspring of the foster-
parents are commonly ejected from the nest within three days after
the cuckoo is hatched ; and as the latter at this age is in a most
helpless condition, Mr. Gould was formerly inclined to believe that
the act of ejection was performed by the foster-parents themselves.
But he has now received a trustworthy account of a young cuckoo
which was actually seen, whilst still blind and not able even to
hold up its own head, in thea£tof_ejectingjjts_fcfiter^^ One

of these was replaced in tKe^nest by the observer, and, was agam
thrown out. With respect to the means by which this strange and
odious instinct was acquired, if it were of great importance for the
young cuckoo, as is probably the case, to receive as much food a9
possible soon after birth, I can see no special difficulty in its having
gradually acquired, during successive generations, the ^bjiftd. desire,,^
the strength, and structure necessary for the work of ejection ; for
those young cuckoos which had such habits and structure best deve-
loped would be the most securely reared. The first step towards
the acquisition of the proper instinct might have been mere unin-
tentional restlessness on the part of the young bird, when somewhat
advanced in age and strength ; the habit having been afterwards
improved, and transmitted to an earlier age. I can see no more
difficulty in this, than in the unhatched young cf other birds ac-
•quiring the instinct to break through their own shells ; — or than in
young snakes acquiring in their upper jaws, as Owen has remarked,
a transitory sharp tooth for cutting through the tough egg-shelU
For if each part is liable to individual variations at all ages, and the
variations tend to be inherited at a corresponding or earlier age, — •
propositions which cannot be disputed, — then the instincts and
structure of the young could be slowly modified as surely as thor.e ol
the adult ; and both cases must stand or fall together with the whole
theory of natural selection.

Chap VIII.] INSTINCTS OF THE MOLOTHRUS. 215

Some species of Molothrus, a widely distinct genus of American
birds, allied to our starlings, have parasitic habits like those of the
cuckoo ; and the species present an interesting gradation in the per-
fection of their instincts. The sexes of Molothrus badius are stated
by an excellent observer, Mr. Hudson, sometimes to live promis-
cuously together in flocks, and sometimes to pair. They either
build a nest of their own, or seize on one belonging to some other
bird, occasionally throwing out the nestlings of the stranger. They
either lay their eggs in the nest thus appropriated, or oddly enough
build one for themselves on the top of it. They usually sit on
their own eggs and rear their own young ; but Mr. Hudson says
it is probable that they are occasionally parasitic, for he has seen
the young of this species following old birds of a distinct kind
and clamouring to be fed by them. The parasitic habits of another
species of Molothrus, the M. bonariensis, are much more highly
developed than those of the last, but are still far from perfect.
This bird, as far as it is known, invariably lays its eggs in the
nests of strangers ; but it is remarkable that several together
sometimes commence to build an irregular untidy nest of their
own, placed in singularly ill-adapted situations, as on the leaves
of a large thistle. They never, however, as far as Mr. Hudson
has ascertained, complete a nest for themselves. They often lay
so many eggs — from fifteen to twenty — in the same foster-nest,
that few or none can possibly be hatched. They have, moreover,
the extraordinary habit of pecking holes in the eggs, whether oi
their own species or of their foster-parents, which they find in the
appropriated nests. They drop also many eggs on the bare ground,
which are thus wasted. A third species, the M. pecoris of North
America, has acquired instincts as perfect as those of the cuckoo,
for it never lays more_thajQjone egg_in.a foster^
young bird is securely reared. Mr. Hudson is a strong disbeliever
in evolution, but he appears to have been so much struck by the
imperfect instincts of the Molothrus bonariensis that he quotes my
words, and asks, " Must we consider these habits, not as especially
endowed or created instincts, but as small consequences of one
general bw, namely, transition?"

Various birds, as has already been remarked, occasionally lay
their eggs in the nests of other birds. This habit is not very
uncommon with the Gallinaceje, and throws some light on the
singular instinct of the ostrich. In this family several hen-birds
unite and lay first a few eggs in one nest and then in another ; and
these are hatched by the males. This instinct may probably be
accounted for by the fact of the hens laying a large number of eggs,

216 SPECIAL INSTINCTS. [Chap. VIII.

but, as with the cuckoo, at intervals of two or three days. The
instinct, however, of the American ostrich, as in the case of the Mol-
othrus bonariensis, has not as yet been perfected ; for a surprising
number of eggs lie strewed over the plains, so that in one day's
hunting I picked up no less than_twentjr JjDstjmd wasted_eggs.

Many bees are parasitic, and regularly lay their eggs in the nests
of other kinds of bees. This case is more remarkable than that of
the cuckoo ; for these bees have not only had their instincts but
their structure modified in accordance with their parasitic habits ;
for they do not possess the pollen-collecting apparatus which would
have been indispensable if they had stored up food for their own
young. Some species of Sphegida^ (wasp-like insects) are likewise
parasitic ; and M. Fabre has lately shown good reason for believing
that, although the Tachytes nigra generally makes its own burrow
and stores it with paralysed prey for its own larva?, yet that, wdien
this insect finds a T)iirrow~ already made and stored by another
sphex, it takes advantage of the prize, and becomes for the occasion
parasitic. In this case, as with that of the Molothrus or cuckoo, I
can see no difficulty in natural selection making an occasional habit
permanent, if of advantage to the species, and if the insect whose
nest and stored food are feloniously appropriated, be not thus exter-
minated.

Slave-making instinct. — This remarkable instinct was first dis-
covered in the Formica (Polyerges) rufescens by Pierre Huber, a
better observer even than his celebrated father. This ant is abso-
lutely dependent on its slaves ; without their aid, the species would
certainly become extinct in a single year. The males and fertile
females do no work of any kind, and the workers or sterile females,
though most energetic and courageous in capturing slaves, do no
other work. They are incapable of making their own nests, or of
feeding their own larvse. When the old nest is found inconvenient,
and they have to migrate, it is the slaves which determine the
migration, and actually carry their masters in their jaws. So utterly
helpless are the masters, that when Huber shut up thirty of them
without a slave, but with plenty of the food which they like best,
and with their own larvae and pupse to stimulate them to work, they
did nothing; they could not even feed themselves, and many perished
of hunger. Huber then introduced a single slave (F. lusca), and she
instantly set to work, fed and saved the survivors ; made some cells
and tended the larvse, and put all to rights. What can be more extra-
ordinary than these well-ascertained facts ? If we had not known of
any other slave-making ant, it would have been hopeless to FpecnJate
how so wonderful an instinct could have been perfected.

Chap. VIII.] SLAVE-MAKING INSTINCT. 2 1 7

Another species, Formica sanguinea, was likewise first discovered
by P. Huber to be a slave-making ant. This species is found in
the southern parts of England, and its habits have been attended
to by Mr. F. Smith, of the British Museum, to whom I am much
indebted for information on this and other subjects. Althou^^h
fully trusting to the statements of Huber and Mr. Smith, I tried to
approach tbe subject in a sceptical frame of mind, as any one may
well be excused for doubting the existence of so extraordinary an
instinct as that of making slaves. Hence, I will give the observa-
tions which I made, in some little detail. I opened fourteen nests
of F. sanguinea, and found a few slaves in all. Males and fertile
females of the slave species (F. fusca) are found only in their own
proper communities, and have never been observed in the nests oi
F. sanguinea. The slaves are_black and not above half the size
of theirredmaste/s, so that the contrast in their a^)earancelir
great when tlTe'nest is slightly disturbed, the slaves occasionally
come out, and like their masters are much agitated and defend the
nest : when the nest is much disturbed, aud the larvae and pup^e
are exposed, the slaves work energetically together with their
masters in carrying them away to a place of safety. Hence, it is
clear, that the slayes.feel quite at home. During the months ot
June and July, on three successive years, I watched for many hours
several nests in Surrey and Sussex, and never saw a slave either
leave or enter a nest. As, during these months, the slaves are very
few in number, I thought that they might behave differently when
more numerous ; but Mr. Smith informs me that he has watched
the nests at various hours during May, June, and August, both in
Surrey and Hampshire, and has never seen the slaves, though
present in large numbers in August, either leave or enter the nest.
Hence he considers them as strictly household slaves. The masters,
on the other hand, may be constantly seen bringing in materials for
the nest, and food of all kinds. During the year 1860, however,
in the month of July, I came across a community with an unusually
large stock of slaves, and I observed a few slaves mingled with
their masters leaving the nest, and marching along the same road
to a tall Scotch-fir-tree, twenty-five yards distant, which they
ascended together, probably in search of aphides or cocci. According
to Huber, who had ample opportunities for observation, the slaves
in Switzerland habitually work with their masters in making the
nest, and they alone open and close the doors in the morning and
evening; and, as Huber expressly states, their" principal office is
to^^s^rch for aphides. This difference in the usual habits of the
lijasters and slaves in the two countries, probably depends merely

218 SPECIAL INSTINCTS. [Chap. VIII.

on the slaves being captured in greater numbers in Switzerland
than in England.

One day I fortunately witnessed a migration of F. sanguinea from
one nest to another, and it was a most interesting spectacle to
behold the masters carefully carrying their slaves in their jaws
instead of being carried by them, as in the case of F. rufescens
Another day my attention was struck by about a score of the slave-
makers haunting the same spot, and evidently not in search of
food ; they approached and were vigorously repulsed by an inde-
pendent community of the slave-species (F. fusca) ; sometimes as
many as three of these ants clinging to the legs of the slave-making
F. sanguinea. The latter ruthlessly killed their small opponents,
and carried their dead bodies as food to their nest, twenty-nine yards
distant; but they were prevented from getting any^pupseTo" rear
as slaves. I then dug up a small parcel of the pupas of F. fusca
from another nest, and put them down on a bare spot near the
place of combat ; they were eagerly seized and carried off by the
tyrants, who perhaps fancied that, after all, they had been victorious
in their late combat.

At the same time I laid on the same place a small parcel of the
pupas of another species, F. flava, with a few of these little yellow
ants still clinging to the fragments of their nest. This species is
sometimes, though rarely, made into slaves, as has been described
by Mr. Smith. Although so small a species, it is very courageous,
and I have seen it ferociously attack other ants. In one instance
I found to my surprise an independent community of F. flava
under a stone beneath a nest of the slave-making F. sanguinea ;
and when I had accidentally disturbed both nests, the little ants
attacked their big neighbours with surprising courage. Now I was
curious to ascertain whether F. sanguinea could distinguish the
pup£e of F. fusca, which they habitually make into slaves, from
those of the little and furious F. flava, which they rarely capture,
and it was evident that they did _at once distinguish them ; for
we have seen that they eagerly and instantly seized the pupaj of
F. fusca, whereas they were much terrified when they came across
the pupa3, or even the earth from the nest, of F. flava, and quickly
ran away ; but in about a quarter of an hour, shortly after all the
little yellow ants had crawled away, they took heart and carried
off the pup£e.

One evening I visited another community of F. sanguinea, and
found a number of these ants returning home and entering their
nests, carrying the dead bodies of F. fusca (showing that it w&s not
a migration) and numerous pupse. I traced a long file ol ants

CiiAP. VIII.] SLAVE-MAKING INSTINCT. 219

burthened withjDOotj, for about tjortj yards back, to a very thick
clump of heath, whence I saw the last individual of" F. sanguinea
emerge, carrying a pupa ; but T was not able to find the desolated
nest in the thick heath. The nest, however, must have been close
at hand, for two or three individuals of F. fusca were rushing about
in the greatest agitation, and one was perched motionless with its
own pupa in its mouth on the top of a spray of heath, an image
of despair over its ravaged home.

Such are the facts, though they did not need confirmation by me,
in regard to the wonderful instinct of making slaves. Let it be
observed what a contrast the instinctive habits of F. sanguinea
present with those of the continental F. rufescens. The latter does
not build its own nest, does not determine its own migrations, does
not collect food for itself or its young, and cannot even feed itself :
it is absolutely dependent_on_Jts numerous slaves. Formica san-
guinea, on the other hand, possesses much fewer slaves, and in the
early part of the summer extremely few : the masters determine
when and where a new nest shall be formed, and when they
migrate, the masters carry the slaves. Both in Switzerland and
England the slaves seem to have the exclusive care of the larvse,
and the masters aJone go on slave-making expeditions. In Switzer-
land the slaves and masters work together, making and bringing
materials for the nest; both, but chiefly the slaves, tend, and
milk, as it may be called, their aphides ; and thus both collect
food for the community. In England the masters alone usually
leave the nest to collect building materials and food for themselves,
their slaves and larvae. So that the masters in this country receive
much less service from their slaves than they do in Switzerland.

By what steps the instinct of F. sanguinea originated I will not
pretend to conjecture. But as ants, which are not slave-makers
will, as I have seen, carry off the pupse of other species, if scattered
near their nests, it is possible that such pup^e originally stored as
food might become developed ; and the foreign ants thus uninten-
tionally reared would then follow their proper instincts, and do what
work they could. If their presence proved useful to the species
which had seized them — if it were more advantageous to this
species to capture workers than to procreate them — the habit of
collecting pupae, originally for food, might by natural selection be
strengthened and rendered permanent for the very different purpose
of raising slaves. When tb3 instinct was once acquired, if carried
out to a much less extent 3ven than in our British F. sanguinea,
which, as we have seen, is less aided by its slaves than the same
Epecies in Switzerland, natural selection might increase and modify

220 SPECIAL INSTINCTS. [Chap Vlil.

the instinct — always supposing each modification to be of use to the
species —until an ant was formed as abjectly dependent on its
slaves as is the Formica rufescens.

Cell-making instinct of the Hive-Bee. — I will not here enter on
minute details on this subject, but will merely give an outline ol
the conclusions at which I have arrived. He must be a dull man
who can examine the exquisite structure of a comb, so beautifully
adapted to its end, without enthusiastic admiration. We hear from
mathematicians that'l)ees have practically^solyed a recondite pro-
blem, and have made their cells of the proper shape To hold tlie
greatest possible amount of honey, with the least possible coa.:^
sumption of precious wax in their construction. It has been re-
marked that a skilful workman with fitting tools and measures,
would find it very difficult to make cells of wax of the true form,
though this is efi"ected by a crowd of bees working in a dark hive.
Granting whatever instincts you please, it seems at first quite
inconceivable how they can make all the necessary angles and
planes, or even perceive when they are correctly made. But the
difiiculty is not nearly so great as it at first appears : all this
beautiful work can be shown, I think, to follow from a few simple
instincts.

I was led to investigate this subject by Mr. Waterhouse, who has
shown that the form of the cell stands in close relation to the
presence of adjoining cells ; and the following view may, perhaps,
be considered only as a modification of his theory. Let us look
to the great principle of gradation, and see whether Nature does
not reveal to us her methoH^oTwork. At one end of a short series
we have humble-bees, which use their old cocoons to hold_honey,
sometimes adding to them short tubes of wax, and li^wise making
separate and very irregular rounded cells of wax. At the other end
of the series we have the cells of the hive-bee, placed in a double
layer: each cell, as is well known, is an hexagonal prism, with
the basal edges of its six sides bevelled so as to join an inverted
pyramid, of three rhombs. These rhombs have certain angles, and
the three which form the pyramidal base of a single cell on one
side of the comb enter into the composition of the bases of three
adjoining cells on the opposite side. In the series between the
extreme perfection of the cells of the hive-bee and the simplicity
of those of the hnmble-bee we have the cells of the Mexican
Melipona domestica^ carefully described and figured by Pierre Huber.
The Melipona itself is intermediate in structure between the hive
and hrimble bee, but more nearly related to the latter ; it fcrms a
nearly regular waxen comb of cylindrical cells, in which the young

Chap. VIIL] CELL-MAKING INSTINCT. 221

are hatclied, and, in addition, some large cells of wax foi holding
honey. These latter cells are nearly spherical and of neaily equal
sizes, and are aggregated into an irregular mass. But the im-
portant point to notice is, that these cells are always made at that
degree of nearness to each other that they would have intersected
or broken into each other if the spheres had _been completed; but
this is never permitted, the bees building perfectly flat waUs.pf.wax_
between the spheres whichjhiia_tend to intersect ._Hence, each cell
consists of an outer spherical portion, and of two, three, or more flat
surfaces, according as the cell adjoins two, three, or more other "-^^-^^
cells. When one cell rests on three other cells, which, from the 1^
spheres being nearly of the same size, is very frequently and neces- ,-— *^v— n^
sarily the case, the three flat surfaces are united into ajryramid ; T |

and this pyramid, as Huber has remarked, is manifestly a gross irni- /^ '
tation of the three-sided pyramidal base of the cell of the hive-bee.
-As in the cells of the hive-bee, so here, the three plane surfaces in
any one cell necessarily enter into the construction of three adjoin-
ing cells. It is obvious that the Melipona saves wax, and what
is more important, labour, by this manner of building ; for the flat
walls between the adjoining cells are not double, but are of the
same thickness as the outer spherical portions, and yet each flat
portion forms a part of ^two cells.

Reflecting on this case, irbccurred to me that if the Melipona
had made its spheres at some given distance from each other, and
had made them of equal sizes and had arranged them symmetrically
in a double layer, the resulting structure would have been as per-
fect as the comb of the hive-bee. Accordingly I wrote to Professor
Miller, of Cambridge, and this geometer has kindly read over the
following statement, drawn up from his information, and tells me
that it is strictly correct : —

If a number of equal spheres be described with their centres
placed in two parallel layers ; with the centre of each sphere at the
distance of radius x >v/ 2, or radius x 1*41421 (or at some lesser
distance), from the centres of the six surrounding spheres in the
same layer; and at the same distance from the centres of the ad-
joining spheres in the other and parallel layer ; then, if planes of
intersection between the several spheres in both layers be formed,
there will result a double layer^o^hexagonal^lsms united together
by pyramidal bases formed of three~rhomBs ; and the rhombs and
ihe sides of the hexagonal prisms will have every angle identically
the same with the best measurements which have been made of the
cells of the hive-bee. But I hear from Prof. Wyman, who has
made numerous careful mea? urements, that the accura«Tof the

222 SPECIAL INSTINCTS. [CiiAP. VIII.

workmanship of the bee has been greatly exaggerated ; so much so,
that whatever t^^p- tj7Tjj]{^l^ ^^^^ of the cell may be, it is rarely, if
ever, realised.

Hence we may safely conclude that, if we could slightly modify
the instincts already possessed by the Melipona, and in themselves
not very wonderful, this bee would make a structure as wonderfully
perfect as that of the hive-bee. We must sapposc the Melipona to
have the power of forming her cells truly spherical, and of equal
sizes ; and this would not be very surprising, seeing that she already
does so to a certain extent, and seeing what perfectly cylindrical
burrows many insects make in wodd, apparently by turning round
on a fixed point. We must suppose the Melipona to arrange her
cells in level layers, as she already does her cylindrical cells ; and
we must further suppose, and this is the greatest difficulty, that
she can somehow judge accurately at what distance to stand from
her fellow-labourers when several are making their spheres ; but
she is already so far enabled to judge of distance, that she always
describes her spheres so as to intersect to a certain extent ; and then
she unites the points of intersection by perfectly fiat surfaces. By
such modifications of instincts which in themselves are not very
wonderful, — hardly more wonderful than those which guide a
bird to make its nest, — 1 believe that the hive-bee has acquired,
through natural selection, her inimitable architectural powers.

But this theory can be tested by experiment. Following the
example of Mr. Tegetmeier, I separated two combs, and put between
them a long, thick, rectangular strip of wax: the bees instantly
began to excavate minute circular pits in it ; and as they deepened
these little pits, they made them wider and wider until they were
converted into shallow basins, appearing to the eye perfectly true or
parts of a sphere, and of about the diameter of a cell. It was most
interesting to observe that, wherever several bees had begun to
excavate these basins near together, they had begun their work at
such a distance from each other, that by the time the basins had
acquired the above-stated width (i. e. about the width of an ordinary
cell), and were in depth about one sixth of the diameter of the
sphere of which they formed a part, the rims of the basins intersected
or broke into each other. As soon as this occurred, the bees ceased
to excavate, and began to build up flat walls of wax on the lines of
intersection between the basins, so that each hexagonal prism was
built upon the scalloped edge of a smooth basin, instead of on the
straight edges of a three-sided pyramid as in the case of oidlnary
cells.

I then put into the hive, instead of a thick, rectangular piece of

Chap. VIU.] CELL-MAKING INSTINCT. 223

wax, a thin and narrow, knife-edged ridge, coloured with vermilion.
The bees instantly began on both sides to excavate little basins
near to each other, in the same way as before ; but the ridge of wax
was so thin, that the bottoms of the basins, if they had been exca-
vated to the same depth as in the former experiment, would have
broken into each other from the opposite sides. The bees, however,
did not suffer this to happen, and they stopped their excavations in
due time; so that the basins, as soon as they had been a littln
deepened, came to have flat bases ; and these fiat bases, formed by
thin little plates of the vermilion wax left ungnawed, were situated^
as far as the eye could judge, exactly^ along the planes of imaginary
intersection between the basins on the opposite sides of the ridge
of wax. In "some parts, only small portions, in other parts, large
portions of a rhombic plate were thus left between the opposed
basins, but the work, from the unnatural state of things, had not
been neatly performed. The bees must have worked at very
nearly the same rate in circularly gnawing away and deepening
the basins on both sides of the ridge of vermilion wax, in order to
have thus succeeded in leaving flat plates between the basins, by
stopping work at the planes of intersection.

Considering how flexible thin wax is, I do not see that there is
any difficulty in the bees, whilst at work on the two sides of a strip
)f wax, perceiving when they have gnawed the wax away to the
proper thinness, and then stopping their work. In ordinary combs
t has appeared to me that the bees do not always succeed in work-
ing at exactly the same rate from the opposite sides ; for I have
noticed half-completed rhombs at the base of a just-commenced cell,
which were slightly concave on one side, where I suppose that the
bees had excavated too quickly, and convex on the opposed side
where the bees had worked less quickly. In one well marked
instance, I put the comb back into the hive, and allowed the bees
to go on working for a short time, and again examined the cell, and
I found that the rhombic plate had been completed, and had become
perfectly flat : it was absolutely impossible, from the extreme thin-
ness of the Uttle plate, that they could have effected this by gnawing
away the convex side ; and I suspect that the bees in such cases
stand on opposite sides and push and bend the ductile and warm
wax (which as I have tried is easily done) into its proper inter-
mediate plane, and thus flatten it.

From the experiment of the ridge of vermilion wax we can see
that, if the bees were to build for themselves a thin wall of wax,
they could make their cells of the proper shape, by standing at the
proper distance from each other, by excavating at the same rate.

221 SPECIAL INSTINCTS. [Chap. VIIl.

and by endeavouring to make equal spherical hollows, but never
allowing the spheres to break into each other. Kow bees, a-s may *
be clearly seen by examining the edge of a growing comb,'do make
a rough, circumferential wall or rim all round the comb ; and they
gnaw this away from the opposite sides, always working circularly
as they deepen each cell. They do not make the whole three-sided
pyramidal base of any one cell at the same time, but only that
one rhombic plate which stands on the extreme growing margin, or
the two plates, as the case may be ; and they never complete the
upper edges of the rhombic plates, until the hexagonal walls are
commenced. Some of these statements differ from those made by
the justly celebrated elder Huber, but I am convinced of their
accuracy ; and if I had space, I could show that they are conformable
with my theory.

Huber's statement, that the very first cell is excavated out of a
little par.allel-sided wall of wax, is not, as far as I have seen, strictly
correct ; the first commencement havmg always been a little hood
of wax ; but I will not here enter on details. We see how important
a part excavation plays in the construction of the cells; but it
would be a great error to suppose that the bees cannot build up a
rough wall of wax in the proper position — that is, along the plane
of intersection between two adjoining spheres. I have several spe-
cimens showing clearly that they can do this. Even in the rude
circumferential rim or wall of wax round a growing comb, flexures
may sometimes be observed, corresponding in position to the planes
of the rhombic basal plates of future cells. But the rough wall of
wax has in every case to be finished off, by being largely gnawed
away on both sides. The manner in which the bees build is
curious ; they always make the first rough wall from ten to twenty
times thicker than the excessively thin finished wall of the cell,
which will ultimately be left. "We shall understand how they
work, by supposing masons first to pile up a broad ridge of cement,
and then to begin cutting it away equally on both sides near the
ground, till a smooth, very thin wall is left in the middle ; the
masons always piling up the cut-away cement, and adding fresh
cement on the summit of the ridge. We shall thus have a thin
wall steadily growing upward but always crowned by a gigantic
coping. From all the cells, both those just commenced and those
completed, being thus crowned by a strong coping of wax, the bees
can cluster and crawl over the comb without injuring the delicate
hexagonal walls. These walls, as Professor Miller has kindly ascer-
tained for me, vary greatly in thickness ; being, on an average of
twelve measurements made near the border of the comb, j\^ of ar

Chap. VIIl.l CELL-MAKING INSTINCT. 225

Iflch in thickness; whereas the basal rhomboidal plates are thicker,
nearly in ths proportion of three to two, having a mean thickness
from twenty-one measurements, of 2^ of an inch. By the above
singular manner of building, strength is continually given to the
comb, with the utmost ultimate economy of wax.

It seems at first to add to the difficulty of understanding how
the cells are made, that a multitude of bees all work together ; one
bee after working a short time at one cell going to another, so that,
as Huber has stated, a score of individuals work even at the com-
mencement of the first cell. I was able practically to show this
fact, by covering the edges of the hexagonal walls of a single cell,
or the extreme margin of the circumferential rim of a growing
comb, with an extremely thin layer of melted vermilion wax ; and
I invariably found that the colour was most delicately diffused by
the bees — as delicately as a painter could have done it with his brush
— by atoms of the coloured wax having been taken from the spot
on which it had been placed, and worked into the growing edges of
the cells all round. The vrork of construction seems to be a sort
of balance struck between many bees, all instinctively standing at
the same relative distance from each other, all trying tO sweep equal
spheres, and then building up, or leaving un gnawed, the planes of
intersection between these spheres. It was really curious to note
in cases of difficulty, as when two pieces of comb met at an angle,
how often the bees would pull down and rebuild in different ways
the same cell, sometimes recurring to a shape which they had at
first rejected.

When bees have a place on which they can stand in their proper
positions for working, — for instance, on a slip of wood, placed
directly under the middle of a comb growing downwards, so that
the comb has to be built over one face of the sUp — in this case the
bees can lay the foundations of one wall of a new hexagon, in its
strictly proper place, projecting beyond the other completed cells.
It suffices that the bees should be enabled to stand at their proper
relative distances from each other and from the walls of the last
completed cells, and then, by striking imaginary spheres, they can
build up a wall intermediate between two adjoining spheres ; but,
as far as I have seen, they never gnaw away and finish off the
angles of a cell till a large part both of that cell and of the adjoin-
ing cells has been built. This capacity in bees of laying down
under certain circumstances a rough wall in its proper place between
two just-commenced cells, is important, as it bears on a fact, which
seems at first subversive of the foregoing theory ; namely, that the
cells on the extreme, margin of wasp-combs are sometimes strictly

Q

226 SPECIAL INSTINCTS. _Ciiap. VIU.

hexagonal ; but I have not space here to enter on this subject. Nor
does there seem to me any great difiSculty in a single insect (as in
the case of a queen-wasp) making hexagonal cells, if she were to
work alternately on the inside and outside of two or three cells com-
menced at the same time, always standing at the proper relative
distance from the parts of the cells just begun, sweeping spheres or
cylinders, and building up intermediate planes.

As natural selection acts only by the accumulation of slight
modifications of structure or instinct, each profitable to the indi-
vidual under its conditions of life, it may reasonably be asked, how
a long and graduated succession of modified architectural instincts,
all tending towards the present perfect plan of construction, could
have profited the progenitors of the hive-bee ? I think the answer
is not difficult : cells constructed like those of the bee or the wasp
gain in strength, and save much in labour and space, and in the
materials of which they are constructed. With respect to the for-
mation of wax, it is known that bees are often hard pressed to get
sufficient nectar, and I am informed by Mr. Tegetmeier that it has
been experimentally proved that from twelve to fifteen pounds of
dry sugar are consumed by a hive of bees for the secretion of a
pound of wax ; so that a prodigious quantity of fluid nectar must
be collected and consumed by the bees in a. hive for the secretion
of the wax necessary for the construction of their combs. More-
over, many bees have to remain idle for many days during the
process of secretion. A large store of honey is indispensable to
support a large stock of bees during the winter ; and the security
of the hive is known mainly to depend on a large number of bees
being supported. Hence the saving of wax by largely saying_liDney
and the time consumed iii collecting the honey must be an import-
ant element of success to any family of bees. Of course the success
of the species may be dependent on the number of its enemies, or
parasites, or on quite distinct causes, and so be altogether inde-
pendent of the quantity of honey which the bees can collect. But
let us suppose that this latter circumstance determined, as it pro-
bably often has determined, whether a bee allied to our humble-
bees could exist in large numbers in any country; and let us
further suppose that the community lived through the winter, and
consequently required a store of honey : there can in this case bo
no doubt that it would be an advantage to our imaginary humble-
bee, if a slight modification in her instincts led her to make her
waxen cells near together, so as to intersect a little ; for a wall in
common even to two adjoining cells would save some little labour
and wajt. Hence it would continually be more and more advaa-

Chap. VIII.] CELL-MAKING INSTINCT. 227

tageous to our humble-bees, if they were to make their cells more
and more regular, nearer together, and aggregated into a mass, like
the cells of the Melipona ; for in this case a large part of the
bounding surface of each cell would serve to bound the adjoining
cells, and much labour and wax would be saved. Again, from the
same cause, it would be advantageous to the Melipona, if she were
to make her cells closer together, and more regular in every way
than at present ; for then, as we have seen, the spherical surfaces
would wholly disappear and be replaced by plane surfaces ; and the
Melipona would make a comb as perfect as that of the hive-bee.
Beyond this stage of perfection in architecture, natural selection
could not lead ; for the comb of the hive-bee, as far as we can see,
is absolutely perfect in economising labour and wax.

Thus, as I believe, the most wonderful of all known instincts,
that of the hive-bee, can be explained by natural selection having
taken advantage of numerous, successive, slight modifications of
simpler instincts ; natural selection having, by slow degrees, more
and more perfectly led the bees to sweep equal spheres at a given
distance from each other in a double layer, and to build up and
excavate the wax along the planes of intersection; the bees, of
course, no more knowing that they swept their spheres at one par-
ticular distance from each other, than they know what are the
several angles of the hexagonal prisms and of the basal rhombic
plates ; the motive power of the process of natural selection having
been the construction of cells of due strength and of the proper
size and shape for the larv£e, this being effected with the greatest
possible economy of labour and wax ; that individual swarm which
thus made the best cells with least labour, and least waste of honey
in the secretion of wax, having succeeded best, and having trans-
mitted their newly-acquired economical instincts to new swarms,
which in their tm'n will have had the best chance of succeeding in
the struggle for existence.

Ohjections to the Theory of Natural Selection as ajpplied to Instincts :
Neuter and Sterile Insects.

It has been objected to the foregoing view of the origin of instincts
that " the variations of structure and of instinct must have been
simultaneous and accurately adjusted to each other, as a modifica-
tion in the one without an immediate corresponding change in the
other would have been fatal." The force of this objection rests
entirely on the assumption that the changes in the instincts and
structure are abrupt. To take as an illustration the case of the
larger titmouse (Parus major) alluded to in a previous chapter;

Q 2

228 OBJECTIONS TO THE THEORY [Chap. VIU.

this bird often holds the seeds of the yew between its feet on a
branch, and hammers with its beak till it gets at the kernel. Now
what special difficulty would there be in natural selection preserving
all the slight individual variations in the shape of the beak, which
were better and better adapted to break open the seeds, until a
beak was formed, as well constructed for this purpose as that of
the nuthatch, at the same time that habit, or compulsion, or spon-
taneous variations of taste, led the bird to become more and more
of a seed-eater ? In this case the beak is supposed to be slowly
modified by natural selection, subsequently to, but in accordance
with, slowly changing habits of 'tasteYl)ut let the feet of the tit-
mouse vary and grow larger from correlation with the beak, or
from any other unknown cause, and it is not improbable that such
larger feet would lead the bird to climb more and more until it
acquired the remarkable cUmbing instinct and power of the nut-
hatch. In this case a gradual change of structure is supposed to
lead to changed instinctive habits. To take one more case : few
instincts are more remarkable than that which leads the swift of
the Eastern Islands to make its nest wholly ol jnspissatfid^saliva.
Some birds build their nests of mud, believed to be moistened with
saliva ; and one of the swifts of North America makes its nest (as
I have seen) of sticks agglutinated with saliva, and even with flakes
of this substance. Is it then very improbable that the natural
selection of individual swifts, which secreted more and more saliva,
should at last produce a species with instincts leading it to neglect
other materials, and to make its nest exclusively of inspissated
saliva? And so in other cases. It must, however, be admitted
that in many instances we cannot conjecture whether it was instinct
or structure which first varied.

No doubt many instincts of very difficult explanation could be
opposed to the theory of natural selection — cases, in which we can-
not see how an instinct could have originated ; cases, in which no
intermediate gradations are known to exist ; cases of instinct of
such trifiing importance, that they could hardly have been acted on
by natural selection ; cases of instincts almost identically the same
in animals so remote in the scale of nature, that we cannot account
for their similarity by inheritance from a common progenitor, and
consequently must believe that they were independently acquired
through natural selection. I will not here enter on these several
cases, but will confine myself to one special difficulty, which dt first
appeared to me insuperable, and actually fatal to the whole theory.
I allude to the neuters or sterile females in insect-communities;
for these neuters often differ widelv in instinct and in structure

Chap. VIII.] OF NATURAL SELECTION. 229

from both the males and fertile females, and yet, from being sterile,
they cannot propagate their kind.

The subject well deserves to be discussed at great length, but I
will here take only a single case, that of working or sterile ants.
How the workers have been rendered sterile is a difficulty ; but not
much greater than that of any other striking modification of struc-
ture ; for it can be shown that some insects and other articulate
animals in a state of nature occasionally become sterile; and if
such insects had been social, and it had been profitable to the com-
munity that a number should have been annually bom capable of
work, but incapable of procreation, I can see no especial difficulty
in this having been eff'ected through natural selection. But I must
pass over this preliminary difficulty. The great difficulty lies in
the working ants differing widely from both the males and the
fertile females in structure, as in the shape of the thorax, and in
being destitute of wings and sometimes of eyes, and in instinct.
As far as instinct alone is concerned, the wonderful difference in
this respect between the workers and the perfect females, would
have been better exemplified by the hive-bee. If a working ant or
other neuter insect had been an ordinary animal, I should have
unhesitatingly assumed that all its characters had been slowly
acquired through natural selection ; namely, by individuals having
been born with slight profitable modifications, which were inherited
by the offspring; and that these again varied and again were
selected, and so onwards. But with the working ant we have an
insect diff'ering greatly from its parents, yet absolutely sterile ; so
that it could never have transmitted successively acquired modifica-
tions of structure or instinct to its progeny. It may well be asked
how is it possible to reconcile this case with the theory of natural
selection ?

First, let it be remembered that we have innumerable instances,
both in our domestic productions and in those in a state of nature,
of aU sorts of differences of inherited structure which are correlated
with certain ages, and with either sex. We have differences corre-
lated not only with one sex, but with that short period when the
reproductive system is active, as in the nuptial plumage of many
birds, and in the hooked jaws of the male salmon. We have even
slight differences in the horns of different breeds of cattle in rela-
tion to an artificially imperfect state of the male sex ; for oxen oi
o.ertain breeds have longer horns than the oxen of other breeds,
relatively to tne length of the horns in both the bulls and cows of
these same breeds. Hence I can see no great difficulty in any
character becoming; correlated with the sterile condition of certaia

230 OBJECTIONS TO THE THEORY [Chap. Via

members of insect-communities : the difficulty lies in understanding
how such correlated modifications of structure could have been
slowly accumulated by natural selection.

This difficulty, though appearing insuperable, is lessened, or, as
I believe, disappears, when it is remembered that selection may be
applied to the family, as well as to the individual, and may thus
gain the desired end. Breeders of cattle wish the flesh and fat to
be well marbled together : an animal thus characterised has been
slaughtered, but the breeder has gone with confidence to the same
stock and has succeeded. Such faith may be placed in the power
of selection, that a breed of cattle, always yielding oxen with extra-
ordinarily long horns, could, it is probable, be formed by carefully
watching which individual bulls and cows, when matched, produced
oxen with the longest horns ; and yet no one ox would ever have
propagated its kind. Here is a better and real illustration : accord-
ing to M. Verlot, some varieties of the double annual Stock from
having been long and carefully selected to the right degree, always
produce a large proportion of seedlings bearing double and quite
sterile flowers; but they likewise yield some single and fertile
plants. These latter, by which alone the variety can be propagated,
may be compared with the fertile male and female ants, and tlio
double sterile plants with the neuters of the same community.
As with the varieties of the stock, so with social insects, selection
has been applied to the family, and not to the individual, for the
sake of gaining a serviceable end. Hence we may conclude that
slight modifications of structure or of instinct, correlated with the
sterile condition of certain members of the community, have proved
advantageous : consequently the fertile males and females have
flourished, and transmitted to their fertile offspring a tendency to
produce sterile members with the same modifications. This pro-
cess must have been repeated many times, until that prodigious
amount of difierence between the fertile and sterile females of the
same species has been produced, which we see in many .social
insects.

But we have not as yet touched on the acme ot the difficulty ;
namely, the fact that the neuters of several ants differ, not only
from the fertile females and males, but from each other, sometimes
to an almost incredible degree, and are thus divided into two or even
three castes. The castes, moreover, do not commonly graduate
into each other, but are perfectly well defined ; being as distinct
Irom each other as are any two species of the same genus, or rather
as any two genera of the same family. Thus in Eciton, there are
working and soldier neuters, with jaws and instincts extraordinarily

CiiAP. VIII.l OF NATURAL SELECTION 231

different : in Cryptocerus, the workers of one caste alone carry a
wonderful sort of shield on their heads, the use of which is quite
unknown: in the Mexican Myrmecocystus, the workers of one
caste never leave the nest ; they are fed by the workers of another
caste, and they have an enormously developed abdomen which
secretes a sort of honey, supplying the place of that excreted by the
aphides, or the domestic cattle as they may be called, which our
EuropeaiTahTs gu ard and impri son.

It will indeed be thought that I have an overweening confidence
in the principle of natural selection, when I do not admit that
such wonderful and well-established facts at once annihilate the
theory. In the simpler case of neuter insects all of one caste,
which, as I believe, have been rendered difrerent from the fertile
males and females through natural selection, we may conclude from
the analogy of ordinary variations, that the successive, slight, pro-
fitable modifications did not first arise in all the neuters in the same
nest, but in some few alone; and that by the survival of the
conmiunities with females which produced most neuters having
the advantageous modification, all the neuters ultimately came to
be thus characterised. According to this view we ought occasion-
ally to find in the same nest neuter insects, presenting gradations
of structure ; and this we do find, even not rarely, considering how
few neuter insects out of Europe have been carefully examined.
Mr. F. Smith has shown that the neuters of several British ants
differ surprisingly from each other in size and sometimes in colour ;
and that the extreme forms can be linked together by individuals
taken out of the same nest: I have myself compared perfect
gradations of this kind. It sometimes happens that the larger or
the smaller sized workers are the most numerous ; or that both
large and small are numerous, whilst those of an intermediate size
are scanty in numbers. Formica fiava has larger and smaller
workers, with some few of intermediate size ; and, in this species,
as Mr. F. Smith has observed, the larger workers have simple eyes
(ocelli), which though small can be plainly distinguished, whereas
the smaller workers have their ocelli rudimentary. Having
carefully dissected several specimens of these workers, I can affirm
that the eyes are far more rudimentary in the smaller workers than
can be accounted for merely by their proportionally lesser size ; and
I fully believe, though I dare not assert so positively, that the
workers of intermediate size have their ocelli in an exactly inter-
mediate condition. So that here we have two bodies of sterile
workers in the same nest, differing not only in size, but in their
organs of vision, yst connected by some f3w members in an inter-

232 OBJECTIONS TO NATURAL SELECTION. [Chap. VIIL

mediate condition. I may diiiress by adding, that if the smaller
workers had been the most useful to the community, and those
males and females had been continually selected, which produced
more and more of the smaller workers, until all the workers were
in this condition ; we should then have had a species of ant with
neuters in nearly the same condition as those of Myrmica. For
the workers of Myrmica have not even rudiments of ocelli, thougli
the male and female ants of this genus have well-developed ocelli.

I may give one other case : so confidently did I expect occasion-
ally to find gradations of important structures between the different
castes of neuters in the same species, that I gladly availed myself
of Mr. F. Smith's offer of numerous specimens from the same
nest of the driver ant (Anomma) of West Africa. The reader will
perhaps best appreciate the amount of difierence in these workers,
iDy my giving not the actual measurements, but a strictly accurate
illustration : the difference was the same as if we were to see a set
cf workmen building a house, of whom many were five feet four
inches high, and many sixteen feet high ; but we must in addition
auppose that the larger workmen had heads four instead of three
times as big as those of the smaller men, and jaws nearly fivo
times as big. The jaws, moreover, of the working ants of the
several sizes differed wonderfully in shape, and in the form and
number of the teeth. But the important fact for us is, that,
though the workers can be grouped into castes of different sizes,
yet they graduate insensibly into each other, as does the widely-
different structure of their jaws. I speak confidently on this
latter point, as Sir J. Lubbock made drawings for me, with the
camera lucida, of the jaws which I dissected from the workers of
the several sizes. Mr. Bates, in his interesting * Naturalist on the
Amazons,' has described analogous cases.

AVith these facts before me, I believe that natural selection, by
acting on the fertile ants or parents, could form a species which
should regularly produce neuters, all of large size with one form
of jaw, or all of small size with widely different jaws ; or lastly,
and this is the greatest difSculty, one set of workers of one size
and structure, and simultaneously another set of workers of a dif-
ferent size and structure ; — a graduated series having first been
formed, as in the case of the driver ant, and then the extreme
forms having been produced in greater and greater numbers, through
the survival of the parents which generated them, until none with
an intermediate structure were produced.

An analogous explanation has been given by Mr. Wallace, of
the equally complex case, of certain Malayan Butterflies regularly

Chap. VIIL] SUMMARY. 233

appearing under two or even three distinct female foiins ; and by
Fritz Miiller, of certain Brazilian crustaceans likewise appearing
iinder two widely distinct male forms. But this subject need not
here be discussed.

I have now explained how, as I believe, the wonderful fact of
two distinctly defined castes of sterile workers existing in the
same nest, both widely different from each other and from their
parents, has originated. We can see how useful their production
may have been to a social community of ants, on the same principle
that the division of labour is useful to civilised man. Ants, how-
ever, work by inherited instincts and by inherited organs or tools,
whilst man works by acquired knowledge and manufactured instru-
ments. But I must confess, that, with all my faith in natural
selection, I should never have anticipated that this principle could
have been efficient in so high a degree, had not the case of these neuter
insects led me to this conclusion. I have, therefore, discussed this
case, at some little but wholly insufficient length, in order to show
the power of natural selection, and likewise because this is by far the
most serious special difficulty which my theory has encountered.
The case, also, is very interesting, as it proves that with animals, as
with plants, any amount of modification may be effected by the
accumulation of numerous, slight, spontaneous variations, which
are in any way profitable, without exercise or habit having been
brought into play. For peculiar habits confined to the workers or
sterile females, however long they might be followed, could not
possibly affect the males and fertile females, which alone leave
descendants. I am surprised that no one has hitherto advanced
this demonstrative case of neuter insects, against the well-known
doctrine of inherited habit, as advanced by Lamarck.

Nummary,

I have endeavoured in this chapter briefly to show that the
menial qualities of our jlompi^in animals vary, and that the varia-
tions are inherited. Still more briefly I have attempted to show
that instincts vary slightly in a state of nature. No one will dis-
pute that instincts are of the highest importance to each animah
Therefore there is no real difficulty^ uMeTcTiangmg~cohditions ot life,
in natural selection accumulating to any extent slight modifications
of instinct which are in any way useful. In many cases habit or
use and disuse have probably come into play. I do not pretend
tEat the facts given in this chapter strengthen in any great degree
my tleory ; but none of tho cases ot difficulty, to the best of my
judgment, annihilate it. On the other hand, the fact that instincts

234 SUMMARY. [Chap. VIIL

are not always absolutely perfect and are liable to mistakes : — tliat
no instinct can be shown to have been produced for tho good of
other animals, though animals take advantage of the instincts of
others ; — that the canon in natural "History, of "Natura non facit
saltum," is applicable to instincts as well as to corporeal structure,
and is plainly explicable on the foregoing views, but is other-
wise inexplicable, — all tend to corroborate the theory of natural
selection.

This theory is also strengthened by some few other facts in
regard to instincts ; a-s by that common case of closely allied, but
distinct, species, when inhabiting distant parts of tbe world and
living under considerably different conditions of life, yet often
retaining nearly the same instincts. For instance, we can under-
stand, on the principle of inheritance, bow it is that th.e thrush of
tropical South America lines its nest with mud, in the same peculiar
manner as does our British thrush ; how it is that the Hornbills of
Africa and India have the same extraordinary instinctof plastering,
up and imprisoning the females in a hole in a tree, with only a
small hole left in the plaster through which the males feed them
and their young when hatched ; how it is that the male wrens
(Troglodytes) of North America build "cock-nests," to roost in,
like the males of our Kitty- wrens, — a habit wholly unlike that of
any other known bird. Finally, it may not be a logical deduction,
but to my imagination it is far more satisfactory to look at such
instincts as the young cuckoo ejecting its foster-brothers, — ants
making slaves, — the larvas of ichneumonidse feeding within the
live bodies of caterpillars, — not as specially endowed or created
instincts, but as small consequences of one general law leading to
the advancement of all organic beings, — namely, multiply, vary,
let the strongest live and the weakest die.

Chap. IX.] HYBRIDISM. 235

CHAPTEK IX.

Hybridism.

Difitinction between the sterility of first crosses and of hybrids — Sterility
various in degree, not universal, affected by close interbreeding, re-
moved by domestication — Laws governing the sterility of hybrids —
Sterility not a special endowment, but incidental on other differences,
not accumulated by natural selection — Causes of the sterility of first
crosses and of hybrids — Parallelism between the effects of changed
conditions of life and of crossing — Dimorphism and trimorphism —
Fertility of varieties when crossed and of their mongrel offspring not
universal — Hybrids and mongrels compared independently of their
fertility — Summary.

The view commonly entertained by naturalists is that species, when
intercrossed, have been specially endowed with, sterility, in order to
prevent their confusion. This view certainly seems at first highly
probable, for species living together could hardly have been kept
distinct had they been capable of freely crossing. The subject is
in many ways important for us, more especially as the sterility of
species when first crossed, and that of their hybrid offspring, cannot
have been acquired, as I shall show, by the preservation of suc-
cessive profitable degrees of sterility. It is an incidental result of
differences in the reproductive systems of the parent-species.

In treating this subject, two classes of facts, to a large extent
fundamentally different, have generally been confounded ; namely,
the steriUty of species when first crossed, and the sterility of the
liybrids produced from them.

Pure species have of course their organs of reproduction in a per-
fect condition, yet when intercrossed they produce either few or no
offspring. Hybrids, on the other hand, have their reproductive
organs functionally impotent, as may be clearly seen in the state of
the male element in both plants and animals ; though the formative
organs themselves are perfect in structure, as far as the microscope
reveals. In the first case the two sexual elements which go to form
the embryo are perfect ; in the second case they are either not at all
developed, or are imperfectly developed. This distinction is im-
portant, when the cause of the sterility, which is common to the

236 HYBRIDISM. [Chap. IX

two cases, has to be considered, TLe distinction probably has been
slurred over, owing to the sterility in both cases being looked on as
a special endowment, beyond the province of our reasoning powers.

The fertility of varieties, that is of the forms known or believed
to be descended from common parents, when crossed, and likewise
the fertility of their mongrel offspring, is, with reference to my
theory, of equal importance with the sterility of species ; for it
seems to make a broad and clear distinction between varieties and
species.

Degrees of Sterility. — First, for the sterility of species when
crossed and of their hybrid offspring. It is impossible to study the
several memoirs and works of those two conscientious and admirable
observers, Kolreuter and Gartner, who almost devoted their lives to
this subject, without being deeply impressed with the high gene-
rality of some degree of sterility. Koheuter makes the rule
universal ; but then he cuts the knot, for in ten cases in which he
found two forms, considered by most authors as distinct species,
quite fertile together, he unhesitatingly ranks them as varieties.
Gartner, also, makes the rule equally universal ; and he disputes
the entire fertility of Kolreuter' s ten cases. But in these and in
many other cases, Gartner is obliged carefully to count the seeds,
in order to show that there is anj^ degree of sterility. He always
compares the maximum number of seeds produced by two species
when first crossed, and the maximum produced by their hybrid
offspring, with the average number produced by both pure parent-
species in a state of nature. But causes of serious error here inter-
vene : a plant, to be hybridised, must be castrated, and, what is
often more important, must be secluded in order to prevent pollen
being brought to it by insects from other plants. Nearly all the
plants experimented on by Gartner were potted, and were kept in a
chamber in his house. That these processes are often injurious to
the fertility of a plant cannot be doubted ; for Gartner gives in his
table about a score of cases of plants which he castrated, and
artificially fertilised with their own pollen, and (excluding all cases
such as the Leguminosse, in which there is an acknowledged diffi-
culty in the manipulation) half of these twenty plants had their
fertility in some degree impaired. Moreover, as Gartner repeatedly
crossed some forms, such as the common red and blue pimpernels
(Anagallis arvensis and coerulea), which the best botanists rank as
varieties, and found them absolutely sterile, we may doubt whether
many species are really so sterile, when intercrossed, as he believed.

It is certain, on the one hand, that the sterility of various speciea
when crossed is so different in degree and graduates away so in-

Chap. IX.] DEGREES OF STERILITY. 237

sensibly, and, on the other hand, that the fertility of pure species
is so easily affected by various circumstances, that for all practical
purposes it is most difficult to say where perfect fertility ends and
sterility begins. I think no better evidence of this can be required
than that the two most experienced observers who have ever lived,
namely Kolreuter and Gartner, arrived at diametrically opposite
conclusions in regard to some of the very same forms. It is also
most instructive to compare — but I have not space here to enter on
details — the evidence advanced by our best botanists on the question
whether certain doubtful forms should be ranked as species oi
varieties, with the evidence from fertility adduced by different
hybridisers, or by the same observer from experiments made during
different years. It can thus be shown that neither sterility nor
fertility affords any certain distinction between species and varieties.
The evidence from this source graduates away, and is doubtful in
the same degree as is the evidence derived from other constitutional
and structural differences.

In regard to the sterility of hybrids in successive generations ;
though Gartner was enabled to rear some hybrids, carefully guard-
ing them from a cross with either pure parent, for six or seven, and
in one case for ten generations, yet he asserts positively that their
fertility never increases, but generally decreases greatly and sud-
denly. With respect to this decrease, it may first be noticed that
when any deviation in structure or constitution is common to both
parents, this is often transmitted in an augmented degree to the
offspring ; and both sexual elements in hybrid plants are already
affected in some degree. But I believe that their fertility has been
diminished in nearly all these cases by an independent cause,
namely, by too close interbreeding. I have made so many experi-
ments and collected so many facts, showing on the one hand that
an occasional cross with a distinct individual or variety increases
the vigour and fertility of the offspring, and on the other hand that
very close interbreeding lessens their vigour and fertility, that I
cannot doubt the correctness of this conclusion. Hybrids are seldom
raised by experimentalists in great numbers; and as the parent-
species, or other allied hybrids, generally grow in the same garden,
the visits of insects muat be carefully prevented during the flowering
season: hence hybrids, if left to themselves, will generally be
fertilised during each generation by pollen from the same flower ;
and this would probably be injurious to their fertility, already
lessened by their hybrid origin. I am strengthened in this con-
viction by a remarkable statement repeatedly made by Gartner,
namely, that if even the less fertile hybrids be artificially fertilisal

238 HYBRIDISM. [Chap. IX,

with hybrid pollen of the same kind, their fertility, notwithstanding
the frequent ill effects from manipulation, sometimes decidedly
increases, and goes on increasing. Now, in the process of artificial
fertilisation, pollen is as often taken by chance (as I know from my
own experience) from the anthers of another flower, as from the
anthers of the flower itself which is to be fertilised ; so that a cross
between two flowers, though probably often on the same plant,
would be thus effected. Moreover, whenever complicated experi-
ments are in progress, so careful an observer as Gartner would have
castrated his hybrids, and this would have ensured in each genera-
tion a cross with pollen from a distinct flower, either from the same
plant or from another plant of the same hybrid nature. And thus,
the strange fact of an increase of fertility in the successive genera-
tions of artificially fertilised hybrids, in contrast with thoso
spontaneously self-fertilised, may, as I believe, be accounted for by
too close interbreeding having been avoided.

Now let us turn to the results arrived at by a third most experi-
enced hybridiser, namely, the Hon. and Kev. W. Herbert. He is
as emphatic in his conclusion that some hybrids are perfectly fertile
— as fertile as the pure parent-species — as are Kolreuter and Gartner
that some degree of sterility between distinct species is a universal
law of nature. He experimented on some of the very same species
as did Gartner. The difference in their results may, I think, be in
part accounted for by Herbert's great horticultural skill, and by his
having hot-houses at his command. Of his many important state-
ments I will here give only a single one as an example, namely,
that " every ovule in a pod of Crinum capense fertilized by 0.
revolutum produced a plant, which I never saw to occur in a case
of its natural fecundation." So that here we have perfect or even
more than commonly perfect fertility, in a first cross between two
distinct species.

This case of the Crinum leads me to refer to a singular fact,
namely, that individual plants of certain species of Lobelia, Yer-
bascum and Passiflora, can easily be fertilised by pollen from a
distinct species, but not by pollen from the same plant, though this
pollen can be proved to be perfectly sound by fertilising other plants
or species. In the genus Hippeastrum, in Corydalis as shown by
Professor Hildebrand, in various orchids as shown by Mr. Scott and
Fritz Miiller, all the individuals are in this peculiar condition. So
that with some species, certain abnormal individuals, and in other
species all the individuals, can actually be hybridised much more
readily than they can be fertilised by pollen from the same individual
plant ! To gire one instance, a bulb of Hippeastrum aulicum pro-

Jhap. IX.] DEGREES OF STERILITY. 239

duced four flowers ; three were fertilised by Herbert with their own
pollen, and the fourth was subsequently fertilised by the pollen of
a compound hybrid descended from three distinct species : the
result was that " the ovaries of the three first flowers soon ceased to
"grow, and after a few days perished entirely, whereas the pod
" impregnated by the pollen of the hybrid made vigorous growth
" and rapid progress to maturity, and bore good seed, which vege-
" tated freely." Mr. Herbert tried similar experiments during many
years, and always with the same result. These cases serve to show
on what slight and mysterious causes the lesser or greater fertility
of a species sometimes depends.

The practical experiments of horticulturists, though not made
with scientific precision, deserve some notice. It is notorious in
how complicated a manner the species of Pelargonium, Fuchsia,
Calceolaria, Petunia, Khododendron, &c«, have been crossed, yet
many of these hybrids seed freely. For instance, Herbert asserts
that a hybrid from Calceolaria integrifolia and plantaginea, species
most widely dissimilar in general habit, " reproduces itself as per-
fectly as if it had been a natural species from the mountains of
Chili." 1 have taken some pains to ascertain the degree of fertility
of some of the complex crosses of Khododendrons, and I am assured
that many of them are perfectly fertile. Mr. C. Noble, for instance,
informs me that he raises stocks for grafting from a hybrid between
Rhod. ponticum and catawbiense, and that this hybrid '* seeds as
freely as it is possible to imagine." Had hybrids, when fairly
treated, always gone on decreasing in fertility in each successive
generation, as Gartner believed to be the case, the fact would have
been notorious to nursery-men. Horticulturists raise large beds of
the same hybrid, and such alone are fairly treated, for by insect
agency the several individuals are allowed to cross freely with each
other, and the injurious influence of close interbreeding is thus
prevented. Any one may readily convince himself of the efficiency
of insect-agency by examining the flowers of the more sterile kinds
of hybrid Khododendrons, which produce no pollen, for he will
find on their stigmas plenty of pollen brought from other flowers.

In regard to animals, much fewer experiments have been care-
fully tried than with plants. If our systematic arrangements can
be trusted, that is, if the genera of animals are as distinct from each
other as are the genera of plants, then we may infer that animals
more widely distinct in the scale of nature can be crossed more
easily than in the case of plants ; but the hybrids themselves are,
I think, more sterile. It should, however, be borne in mind that,
owing to few animals breeding freely under confinemsnt, few

240 HYBRIDISM [Chap. IX.

experiments have been fairly tried : for instance, the canary-hird
has been crossed with nine distinct species of finches, but, as tot
one of these breeds freely in confinement, we have no right to
expect that the first crosses between them and the canary, or that
their hybrids, should be perfectly fertile. Again, with respect to
the fertility in successive generations of the more fertile hybrid
animals, I hardly know of an instance in which two families of the
same hybrid have been raised at the same time from different
parents, so as to avoid the ill effects of close interbreeding. On the
contrary, brothers and sisters have usually been crossed in each
successive generation, in opposition to the constantly repeated
admonition of every breeder. And in this case, it is not at all
surprising that the inherent sterility in the hybrids should have
gone on increasing.

Although I know of hardly any thoroughly well-authenticated
cases of perfectly fertile hybrid animals, I have reason to believe
that the hybrids from Cervulus vaginalis and Eeevesii, and from
Phasianus colchicus with P. torquatus, are perfectly fertile. M.
Quatrefages states that the hybrids from two moths (Bombyx
cynthia and arrindia) were proved in Paris to be fertile inter se
for eight generations. It has lately been asserted that two such
distinct species as the hare and rabbit, when they can be got to
breed together, produce offspring, which are highly fertile when
crossed with one of the parent-species. The hybrids from the
common and Chinese geese (A. cygnoides), species which are so
different that they are generally ranked in distinct genera, have
often bred in this country with either pure parent, and in one
single instance they have bred inter se. This was effected by
Mr. Eyton, who raised two hybrids from the same parents, but
from different hatches ; and from these two birds he raised no less
than eight hybrids (grandchildren of the pure geese) from one nest.
In India, however, these cross-bred geese must be far more fertile ;
for I am assured by two eminently capable judges, namely Mr.
Blyth and Capt. Button, that whole flocks of these crossed geese
are kept in various parts of the country ; and as they are kept for
profit, where neither pure parent-species exists, they must certainly
be highly or perfectly fertile.

With our domesticated animals, the various races when crossed
together are quite fertile ; yet in many cases they are descended
from two or more wild species. From this fact we must conclude
either that the aboriginal parent-species at first produced perfectly
fertile hybrids, or that the hybrids subsequently reared under
domestication became quite fertile. This latter alternative, which

Chap. IX.] DEGREES OF STERILITY. 241

was first propounded by Pallas, seems by far the most probable, and
can, indeed, hardly be doubted. It is, for instance, almost certain
that our dogs are descended from several wild stocks ; yet, with
perhaps the exception of certain indigenous domestic dogs of South
America, all are quite fertile together; but analogy makes me
greatly doubt, whether the several aboriginal species would at first
have freely bred together and have i)roduced quite fertile hybrids.
So again I have lately acquired decisive evidence that the
crossed offspring from the Indian humped and common cattle are
inter se perfectly fertile ; and from the observations by Kiitimeyer
on their important osteological differences, as well as from those
by Mr. Blyth on their differences in habits, voice, constitution, &c.,
these two forms must be regarded as good and distinct species.
The same remarks may be extended to the two chief races of
the pig. We must, therefore, either give up the belief of the
universal sterility of species when crossed; or we must look at
this sterility in animals, not as an indelible characteristic, but
as one capable of being removed by domestication.

Finally, considering all the ascertained facts on the intercross-
ing of plants and animals, it may be concluded that some degree
of sterility, both in first crosses and in hybrids, is an extremely
general result ; but that it cannot, under our present state of
knowledge, be considered as absolutely universal.

Laws governing the Sterility of first Crosses and of Hybrids.

We will now consider a little more in detail the laws governing
the sterility of first crosses and of hybrids. Our chief object will
be to see whether or not these laws indicate that species have
been specially endowed with this quality, in order to prevent
their- crossing and blending together in utter confusion. The fol-
lowing conclusions are drawn up chiefly from Gartner's admirable
work on the hybridisation of plants. I have taken much pains
to ascertain how far they apply to animals, and, considering how
scanty our knowledge is in regard to hybrid animals, I have
been surprised to find how generally the same rules apply to both
kingdoms.

It has been already remarked, that the degree of fertility, both
of first crosses and of hybrids, graduates from zero to perfect
fertility. It is surprising in how many curious ways this grada-
tion can be shown ; but only the barest outline of the facts can
here be given. When pollen from a plant of one family is placed
on the stigma of a plant of a distinct family, it exerts no mere
influence than so much inorgaric dust. From this absolute zero of

242 LA'W'S GOVERNING THS STERILITY [Chap. IX.

fertility, the pollen of different species applied to tlie stigma of
some one species of tli3 same genus, yields a perfect gradation in
tlae number of seeds produced, up to nearly complete or even quite
complete fertility ; and, as we have seen, in certain abnormal caseSj
even to an excess of fertility, beyond that which the plant's own
pollen produces. So in hybrids themselves, there are some which
never have produced, and probably never would produce, even with
the pollen of the pure parents, a single fertile seed : but in some of
these cases a first trace of fertility may be detected, by the pollen
of one of the pure parent-species causing the flower of the hybrid to
wither earlier than it otherwise would have done ; and the early
withering of the flower is well known to be a sign of incipient
fertilisation. From this extreme degree of sterility we have self-
fertilised hybrids producing a greater and greater number of seeds
up to perfect fertility.

The hybrids raised from two species which are very difficult
to cross, and which rarely produce any offspring, are generally very
sterile ; but the parallelism between the difficulty of making a first
cross, and the sterility of the hybrids thus produced — two cl'asses of
facts which are generally confounded together — is by no means
strict. There are many cases, in which two pure species, as in the
genus Yerbascum, can be united with unusual facility, and produce
numerous hybrid-offspring, yet these hybrids are remarkably sterile.
On the other hand, there are siDccies which can be crossed very
rarely, or with extreme difficulty, but the hybrids, when at last
produced, are very fertile. Even within the limits of the same
genus, for instance in Dianthus, these two OjDposite cases occur.

The fertility, both of first crosses and of hybrids, is more easily
affected by unfavourable conditions, than is that of pure species.
But the fertility of first crosses is likewise innately variable ; for
it is not always the same in degree when the same two species are
crossed under the same circumstances ; it depends in part upon the
constitution of the individuals which happen to have been chosen
for the experiment. So it is with hybrids, for their degree of
fertility is often found to differ greatly in the several individuals
raised from seed out of the same capsule and exposed to the same
conditions.

By the term systematic affinity is meant, the genera] resemblance
between species in structure and constitution. Now the fertility of
first crosses, and of the hybrids produced from them, is largely
governed by their systematic affinity. This is clearly shown by
hybrids never having been raised between species ranked by sys-
tematists in distinct families j and on the other hand, by very

Chap. IX.] OF FIRST CROSSES AND OF HYBRIDS. 243

closely allied species generally uniting with facility. But the
correspondence between systematic affinity and the facility of
crossing is by no means strict. A multitude of cases could be given
of very closely allied species which will not unite, or only with
extreme difficulty ; and on the other hand of very distinct species
which unite with the utmost facility. In the same family there
may be a genus, as Dianthus, in which very many species can most
readily be crossed ; and another genus, as Silene, in which the most
persevering efforts have failed to produce between extremely close
species a single hybrid. Even within the limits of the same genus,
we meet with this same difference ; for instance, the many species ol
Nicotiana have been more largely crossed than the species of almost
any other genus ; but Gartner found that N. acuminata, which is
not a particularly distinct species, obstinately failed to fertilise, or
to be fertilised by no less than eight other species of Nicotiana.
Many analogous facts could be given.

No one has been able to point out what kind or what amount of
difference, in any recognisable character, is sufficient to prevent two
species crossing. It can be shown that plants most widely different in
habit and general appearance, and having strongly marked differ-
ences in every part of the flower, even in the pollen, in the fruit,
and in the cotyledons, can be crossed. Annual and perennial plants,
deciduous and evergreen trees, plants inhabiting different stations
and fitted for extremely different climates, can often be crossed
with ease.

By a reciprocal cross between two species, I mean the case,
for instance, of a female-ass being first crossed by a stallion, and
then a mare by a male-ass : these two species may then be said
to have been reciprocally crossed. There is often the widest
possible difference in the facility of making reciprocal crosses.
Such cases are highly important, for they prove that the capacity
in any two species to cross is often completely independent of their
systematic affinity, that is of any difference in their structure
or constitution, excepting in their reproductive systems. The
diversity of the result in reciprocal crosses between the same two
species was long ago observed by Kolreuter. To give an instance :
Mirabilis jalapa can easily be fertilised by the pollen of M. longi-
flora, and the hybrids thus x^roduced are sufficiently fertile ; but
Kolreuter tried more than two hundred times, during eight fol-
lowing years, to fertilise reciprocally M. longiflora with the pollen of
M. jalapa, and utterly failed. Several other equally striking cases
could be given. Thuret has observed the same fact with certain
sea- weeds or Fuci. Gartner, moreover, found that this difference of

K 2

244 LAWS GOVERNING THE STERILITY [Chap. IX,

facility in making reciprocal crosses is extremely common in a
lesser degree. He has observed it even between closely related
forms (as Matthiola annua and gJabra) which many botanists rank
only as varieties. It is also a remarkable fact, that hybrids raised
from reciprocal crosses, though of course compounded of the very
same two species, the one species having first been used as the
father and then as the mother, though they rarely differ in external
characters, yet generally differ in fertility in a small, and occa-
sionally in a high degree.

Several other singular rules could be given from Gartner : foT
instance, some species have a remarkable power of crossing with
other species ; other species of the same genus have a remarkable
power of impressing their likeness on their hj'^brid offspring ; but
these two powers do not at all necessarily go together. There are
certain hybrids which, instead of having, as is usual, an intermediate
character between their two parents, always closely resemble one of
them ; and such hybrids, though externally so like one of their pure
parent-species, are with rare exceptions extremely sterile. So again
amongst hybrids which are usually intermediate in structure
between their parents, exceptional and abnormal individuals some-
times are bom, which closely resemble one of theii pure parents ;
and these hybrids are almost always utterly sterile, even when the
other hybrids raised from seed from the same capsule have a con-
iiiderable degree of fertility. These facts show how completely the
fertility of a hybrid may be independent of its external resemblance
to either pure parent.

Considering the several rules now given, which govern the
fertility of first crosses and of hybrids, we see that when forms,
which must be considered as good and distinct species, are united,
their fertility graduates from zero to perfect fertility, or even to
fertility under certain conditions in excess; that their fertility,
besides being eminently susceptible to favourable and unfavourable
conditions, is innately variable ; that it is by no means always
the same in degree in the first cross and in the hybrids produced
from this cross ; that the fertility of hybrids is not related to the
degree in which they resemble in external appearance either parent ;
and lastly, that the facility of making a first cross between any
two species is not always governed by their systematic affinity or
degree of resemblance to each other. This latter statement is
clearly proved by the difference in the result of reciprocal cresses
between the same two species, for, according as the one species
or the other is used as the father or the mother, there is generally
Bome diffefence, and occasionally the widest possible difference^

Chap. IX.] OF FIRST CROSSES AND OF HYBRIDS. 245

ia the facility of effecting an union. The hybrids, moreover,
produced from reciprocal crosses often differ in fertility.

Now do these complex and singular rules indicate that species
have been endowed with sterility simply to prevent their becoming
confounded in nature ? I think not. For why should the sterility
be so extremely different in degree, when various species are crossedj
all of which we must suppose it would be equally important to keep
from blending together? Why should the degree of sterility be
innately variable in the individuals of the same species? Why
should some species cross with facility, and yet produce very sterile
hybrids ; and other species cross with extreme difficulty, and yet
produce fairly fertile hybrids? Why should there often be so
great a difference in the result of a reciprocal cross between the
same two species ? Why, it may even be asked, has the production
of hybrids been permitted ? To grant to species the special power
of producing hybrids, and then to stop their further propagation by
different degrees of sterility, not strictly related to the facility of
the first union between their parents, seems a strange arrangement.

The foregoing rules and facts, on the other hand, appear to me
clearly to indicate that the sterility both of first crosses and of
hybrids is simply incidental or dependent on unknown differences
in their reproductive systems ; the differences being of so peculiar
and limited a nature, that, in reciprocal crosses between the same
two species, the male sexual element of the one will often freely act
on the female sexual element of the other, but not in a reversed
direction. It will be advisable to explain a little more fully by
an example what I mean by sterility being incidental on other
differences, and not a specially endowed quality. As th-e capacity
of one plant to be grafted or budded on another is unimportant for
their welfare in a state of nature, I presume that no one will suppose
that this capacity is a specially endowed quality, but will admit that
it is incidental on differences in the laws of growth of the two
plants. We can sometimes see the reason why one tree will not
take on another, from differences in their rate of growth, in the
hardness of their wood, in the period of the flow or nature of their
sap, &c. ; but in a multitude of cases we can assign no reason what-
ever. Great diversity in the size of two plants, one being woody
and the other herbaceous, one being evergreen and the other deci-
duous, and adaptation to widely different climates, do not always
prevent the two grafting together. As in hybridisation, so with
grafting, the capacity is limited by systematic affinity, for no one
has been able to graft together trees belonging to quite distinct
families ; and, on the other hand, closely allied species, and varieties

240 LAWS GOVERNING STERILITY. [Chap. IX

of the same species, can usually, but not invariably, be grafted -with
ease. But this capacity, as in hybridisation, is by no means abso-
lul^ly governed by systematic afiSnity. Although many distinct
genera within the same family have been grafted together, in other
cases species of the same genus will not take on each other. The
pear can be grafted far more readily on the quince, which is ranked
as a distinct genus, than on the apple, which is a member of the
same genus. Even different varieties of the pear take with different
degrees of facility on the quince ; so do different varieties of the
apricot and peach on certain varieties of the plum.

As Gartner found that there was sometimes an innate difference
in different individuals of the same two species in crossing ; so
Sageret believes this to be the case with different individuals of
the same two species in being grafted together. As in reciprocal
crosses, the facility of effecting an union is often very far from
equal, so it sometimes is in grafting ; the common gooseberry, for
instance, cannot be grafted on the currant, whereas the currant will
take, though with difficulty, on the gooseberry.

We have seen that the sterility of hybrids, which have their
reproductive organs in an imperfect condition, is a different case
from the difficulty of uniting two pure species, which have their
reproductive organs perfect ; yet these two distinct classes of
cases run to a large extent parallel. Something analogous occurs
in grafting ; for Thoum found that three species of Eobinia,
which seeded freely on their own roots, and which could be
grafted with no great difficulty on a fourth species, when thus
grafted were rendered barren. On the other hand, certain species of
Sorbus, when grafted on other species yielded twice as much fruit
as when on their own roots. We are reminded by this latter fact of
the extraordinary cases of Hippeastrum. Passi flora, &c., which seed
much more freely when fertilised with the pollen of a distinct
species, than when fertilised with pollen from the same plant.

We thus see, that, although there is a clear and great difference
between the mere adhesion of grafted stocks, and the union of
the male and female elements in the act of reproduction, yet that
there is a rude degree of parallelism in the results of grafting and of
crossing distinct species. And as we must look at the curious
and complex laws governing the facility with which trees can be
grafted on each other as incidental on unknown differences in their
vegetative systems, so I believe that the still more complex laws
governing the facility of first crosses are incidental on unknown
differences in their reproductive systems. These differences in both
cases, follov; to a certain extent, as might have been expected*

Chap. IX.] STERILITY OF HYBRIDS. 247

systematic affinity, by which term every kind of resemblance and
dissimilarity between organic beings is attempted to be expressed.
The facts by no means seem to indicate that the greater or lesser
difficulty of either grafting or crossing various species has been a
special endowment ; although in the case of crossing, the difficulty
is as important for the endurance and stability of specific forma,
as in the case of grafting it is unimportant for their welfare.

Origin and Causes of the Sterility of first Crosses and of

Hyhrids.

At one time it appeared to me probable, as it has to others, that
the sterility of first crosses and of hybrids might have been slowly
acquired through the natural selection of slightly lessened degrees
of fertility^ which, like any other variation, spontaneously appeared
in certain individuals of one variety when crossed with those of
another variety. For it would clearly be advantageous to two
varieties or incipient species, if they could be kept from blending,
on the same principle that, when man is selecting at the same time
two varieties, it is necessary that he should keep them separate.
In the first place, it may be remarked that species inhabiting
distinct regions are often sterile when crossed ; now it could clearly
have been of no advantage to such separated species to have been
rendered mutually sterile, and consequently this could not have
been effected through natural selection ; but it may perhaps be
argued, that, if a species was rendered sterile with some one
compatriot, sterility with other species would follow as a necessary
contingency. In the second place, it is almost as much opposed to
the theory of natural selection as to that of special creation, that in
reciprocal crosses the male element of one form should have been
rendered utterly impotent on a second form, whilst at the same
time the male element of this second form is enabled freely to
fertilise the first form ; for this peculiar state of the reproductive
system could hardly have been advantageous to either species.

In considering the probability of natural selection having come
into action, in rendering species mutually sterile, the greatest
difficulty will be found to lie in the existence of many graduated
steps from slightly lessened fertility to absolute sterility. It may
be admitted that it would profit an incipient species, if it were
rendered in some slight degree sterile when crossed with its parent
form or w^ith some other variety ; for thus fewer bastardised and
deteriorated offspring would be produced to commingle their blood
with the new species in process of formation. But he who will take
the trouble to reflect on the steps by which this first degree of

248 <?AUSES OF THE STERILITY [Chap. IX

sterility could be increased tlirougli natural selection to that high
degree which is common with so many species, and which is
universal with species which have been differentiated to a generic
or family rank, will find the subject extraordinarily complex.
After mature reflection it seems to me that this could not have been
effected through natural selection. Take the case of any two
species which, when crossed, produce few and sterile offspring ; now,
what is there which could favour the survival of those individuals
which happened to be endowed in a slightly higher degree with
mutual infertility, and which thus approached by one small step
towards absolute sterility ? Yet an advance of this kind, if the
theory of natural selection be brought to bear, must have incessantly
occurred with many species, for a multitude are mutually quite
barren. With sterile neuter insects we have reason to believe that
modifications in their structure and fertility have been slowly
accumulated by natural selection, from an advantage having been
thus indirectly given to the community to which they belonged
over other communities of the same species ; but an individual
animal not belonging to a social community, if rendered slightly
sterile when crossed with some other variety, would not thus itself
gain any advantage or indirectly give any advantage to the other
iadividuals of the same variety, thus leading to their preservation.

But it would be superfluous to discuss this question in detail;
for with plants we have conclusive evidence that the sterility of
crossed species must be due to some principle, quite independent of
natural selection. Both Gartner and Kolreuter have proved that in
genera including numerous species, a series can be formed from
species which when crossed yield fewer and fewer seeds, to species
which never produce a single seed, but yet are affected by the
pollen of certain other species, for the germen swells. It is here
manifestly impossible to select the more sterile individuals, which
have already ceased to yield seeds ; so that this acme of sterility,
when the germen alone is affected, cannot have been gained through
selection ; and from the laws governing the various grades of sterility
being so uniform throughout the animal and vegetable kingdoms,
we may infer that the cause, whatever it may be, is the same or
nearly the same in all cases.

We will now look a little closer at the probable nature of ths
differences between species which induce sterility in first crosses
and in hybrids. In the case of first crosses, the greater or lesa
difficulty in effecting an union and in obtaining offspring apparently
depends on several distinct causes. Theie must sometimes be a

Chap. IX.] OF FIRST CROSSES AND OF HYBRIDS. 249

physical impossibility in the male element reaching the ovule, as
would be the case with a plant having a pistil too long for the polkn-
tubes to reach the ovarium. It has also been observed that when
the pollen of one species is placed on the stigma of a distantly allied
species, though the pollen-tubes protrude, they do not penetrate the
stigmatic surface. Again, the male element may reach the female
element but be incapable of causing an embryo to be developed, as
seems to have been the case with some of Thuret's experiments on
Fuci. No explanation can be given of these facts, any more than
why certain trees cannot be grafted on others. Lastly, an embryo
may be developed, and then perish at an early period. This latter
alternative has not been sufficiently attended to ; but I believe,
fi'om observations communicated to me by Mr. Hewitt, who has
had great experience in hybridising pheasants and fowls, that the
early death of the embryo is a very frequent cause of sterility in
first crosses. Mr. Salter has recently given the results of an
examination of about 500 eggs produced from various crosses
between three species of Gallus and their hybrids ; the majority of
these eggs had been fertilised ; and in the majority of the fertilised
eggs, the embryos had either been partially developed and had then
perished, or had become nearly mature, but the young chickens had
been unable to break through the shell. Of the chickens which
were born, mere than four-fifths died within the first few days, or
at latest weeks, " without any obvious cause, apparently from mere
inability to live ;" so that from the 500 eggs only twelve chickens
were reared. With plants, hybridised embryos probably often
perish in a like manner ; at least it is known that hybrids raised
from very distinct species are sometimes weak and dwarfed, and
perish at an early age ; of which fact Max Wichura has recently
given some striking cases with hybrid willows. It may be here
worth noticing that in some cases of parthenogenesis, the embryos
within the eggs of silk mcths v^hich had not been fertilised, pass
through their early stages of development and then perish like the
embryos produced by a cross between distinct species. Until
becoming acquainted with these facts, I was unwilling to believe in
the frequent early death of hybrid embryos ; for hybrids, when
once born, are generally healthy and long-lived, as we see in the
case of the common mule. Hybrids, however, are differently cir-
cumstanced before and after birth : when born and living in a
country where their two parents live, they are generally placed under
suitable conditions of life. But a hybrid partakes of only half of
the nature and constitution of its mother ; it may therefore before
birth, as long as it is nourished within its mother's womb, or within

2.')C CAUSES OF THE STERILITY [Chap. IX.

tlie egg or seed produced by the motlier, be exposed to conditions
in some degree unsuitable, and consequently be liable to perish at
an early period; more especially as all very young beings are
eininently sensitive to injurious or unnatural conditions of life.
But after all, the cause more probably lies in some imperfection in
the original act of impregnation, causing the embryo to be im-
perfectly developed, rather than in the conditions to which it is
subsequently exposed.

In regard to the sterility of hybrids, in vrhich the sexual elements
are imperfectly developed, the case is somewhat different. I have
more than once alluded to a large body of facts showing that, when
animals and plants are removed from their natural conditions, they
are extremely liable to have their reproductive systems seriously
affected. This, in fact^ is the great bar to the domestication of
animals. Between the sterility thus superinduced and that of
hybrids, there are many points of similarity. In both cases the
sterility is independent of general health, and is often accompanied
by excess of size or great luxuriance. In both cases the sterility
occurs in various degrees ; in both, the male element is the most
liable to be affected; but sometimes the female more than the
male. In both, the tendency goes to a certain extent with sys-
tematic affinity, for whole groups of animals and plants are rendered
impotent by the same unnatural conditions ; and whole groups
of species tend to produce sterile hybrids. On the other hand, one
species in a group will sometimes resist great changes of conditions
with unimpaired fertility; and certain species in a group will
produce unusually fertile hybrids. No one can tell, till he tries,
whether any particular animal will breed under confinement, or
any exotic plant seed freely under culture ; nor can he tell till he
tries, whether any two species of a genus will produce more or less
sterilo hybrids. Lastly, when organic beings are placed during
several generations under conditions not natural to them, they are
extremely liable to vary, which seems to be partly due to their
reproductive systems having been specially affected, though in a
lesser degtee than when sterility ensues. So it is with hybrids, for
their offspring in successive generations are eminently liable to vary,
as every experimentalist has observed.

Thus we see that when organic beings are placed under new
and unnatural conditions, and when hybrids are produced by the
unnatural crossing of two species, the reproductive system, inde-
pendently of the general state of health, is affected in a very
similar manner. In the one case, the conditions of life have been
disturbed, though often in so slight a degree as to be inappreciable

Chap. IX.] OF JIRST CEOSSES AND OF HYBRIDS. 251

by us ; in the other case, or that of hybrids, the external conditions
have remained the same, but the organisation has been disturb>3d
by two distinct structures and constitutions, including of course the
reproductive systems, having been blended into one. For it is
scarcely possible that two organisations should be compounded
into one, without some disturbance occurring in the development, or
periodical action, or mutual relations of the different parts and
organs one to another or to the conditions of life. When hybrids
are able to breed inter se, they transmit to their offspring from
generation to generation the same compounded organisation, and
hence we need not be surprised that their sterility, though in some
degree variable, does not diminish ; it is even apt to increase, this
being generally the result, as before explained, of too close inter-
breeding. The above view of the sterility of hybrids being caused
by two constitutions being compounded into one has been strongly
maintained by Max Wichura.

It must, however, be owned that we cannot understand, on the
above or any other view, several facts with respect to the sterility
of hybrids ; for instance, the unequal fertility of hybrids produced
from reciprocal crosses ; or the increased sterility in those hybrids
which occasionally and exceptionally resemble closely either pure
parent. Nor do I pretend that the foregoing remarks go to the
root of the matter ; no explanation is offered why an organism,
when placed under unnatural conditions, is rendered sterile. All
that I have attempted to show is, that in two cases, in some respects
allied, sterility is the common result,— in the one case from the
conditions of life having been disturbed, in the other case from
the organisation having been disturbed by two organisations being
compounded into one.

A similar parallelism holds good with an allied yet veiy different
class of facts. It is an old and almost universal belief founded on a
considerable body of evidence, which I have elsewhere given, that
slight changes in the conditions of life are beneficial to all living
things. We see this acted on by farmers and gardeners in their
frequent exchanges of seed, tubers, &c., from one soil or climate to
another, and back again. During the convalescence of animals,
great benefit is derived from almost any change in their habits of life.
Again, both with plants and animals, there is the clearest evidence
that a cross between individuals of the same species, which differ to
a certain extent, gives vigour and fertility to the offspring ; and
that close interbreeding continued during several generations between
the nearest relations, if these be kept under the same conditions of
life, almost always leads to decreased size, weakness, or sterility.

252 RECIPROCAL DIMORPHISM [Chap. IX.

Hence it seems that, on the one hand, slight changes in the con-
ditions of life benefit all organic beings, and on the other hand, that
slight crosses, that is crosses between the males and females of the
same species, which have been subjected to slightly diffei'ent con-
ditions, or which have slightly varied, give vigour and fertility to
the offspring. But, as we have seen, organic beings long habituated
to certain uniform conditions under a state of nature, when sub-
jected, as under confinement, to a considerable change in their
conditions, very frequently are rendered more or less sterile ; and
we know that a cross between two forms, that have become widel7
or specifically different, produce hybrids which are almost always in
some degree sterile. I am fully persuaded that this double paral-
lelism is by no means an accident or an illusion. He who is able
to explain why the elephant and a multitude of other animals are
incapable of breeding when kept under only partial confinement in
their native country, will be able to explain the primary cause of
hybrids being so generally sterile. He will at the same time be
able to explain hov/ it is that the races of some of our domesticated
animals, which have often been subjected to new and not uniform
conditions, are quite fertile together, although they are descended
from distinct species, which would probably have been sterile if
aboriginally crossed. The above two parallel series of facts seem
to be connected together by some common but unknown bond,
which is essentially related to the principle of life ; this principle,
according to Mr. Herbert Spencer, being that life depends on, or
consists in, the incessant action and reaction of various forces,
which, as throughout nature, are always tending towards an equi-
librium; and when this tendency is slightly disturbed by any
change, the vital forces gain in power.

Reciprocal Dimorphism and Trimorjpldsm.

This subject may be here briefly discussed, and will be found to
throw some light on hybridism. Several plants belonging to
distinct orders present two forms, which exist in about equal
numbers and which differ in no respect except in their reproductive
organs ; one form having a long pistil with short stamens, the other
a short pistil with long stamens ; the two having differently sized
pollen-grains. With trimorphic plants there are three forms like-
wise differing in the lengths of their pistils and stamens, in the size
and colour of the pollen-grains, and in some other respects ; and as
in each of the three forms there are two sets of stamens, the three
foi-ms possess altogether six sets of stamens and three kinds of
pistils. These organs are so proportioned iji length to each other^

Chap. IX.] AND TRIMORPHISM. 253

that half the stamens in two of the forms stand on a level with
the stigma of the third form. Now I have shown, and the result
has been confirmed by other observers, that, in order to obtain full
fertility with these plants, it is necessary that the stigma of the one
form should be fertilised by pollen taken from the stamens of cor-
responding height in another form. So that with dimorphic species
'WO unions, which may be called legitimate, are fully fertile ; and
two, which may be called illegitimate, are more or less infertile.
With trimorphic species six unions are legitimate or fully fertile,
and twelve are illegitimate or more or less infertile.

ITie infertility which may be observed in various dimorphic and
trimorphic plants, when they are illegitimately fertilised, that is by
pollen taken from stamens not corresponding in height with the
pistil, dififers much in degree, up to absolute and utter sterility ; just
in the same manner as occurs in crossing distinct species. As the
degree of sterility in the latter case depends in an eminent degree
on the conditions of life being more or less favourable, so I have
found it with illegitimate unions. It is well known that if pollen
of a distinct species be placed on the stigma of a flower, and its own
pollen be afterwards, even after a considerable interval of time,
placed on the same stigma, its action is so strongly prepotent that
it generally annihilates the effect of the foreign pollen ; so it is with
the pollen of the several forms of the same species, for legitimate
pollen is strongly prepotent over illegitimate pollen, when both are
placed on the same stigma. I ascertained this by fertilising several
flowers, first illegitimately, and twenty-four hours afterwards legiti-
mately, with pollen taken from a peculiarly coloured variety, and
all the seedlings were similarly coloured ; this shows that the
legitimate pollen, though applied twenty-four hours subsequently,
had wholly destroyed or prevented the action of the previously
applied illegitimate pollen. Again, as in making reciprocal crosses
between the same two species, there is occasionally a great difference
in the result, so the same thing occurs with trimorphic plants ; for
instance, the mid-styled form of Lythrum salicaria was illegitimately
fertilised with the greatest ease by pollen from the longer stamens
of the short-styled form, and yielded many seeds ; but the latter
form did not yield a single seed when fertilised by the longer
stamens of the mid-styled form.

In all these respects, and in others which might be added, the
forms of the same undoubted species when illegitimately united
behave in exactly the same manner as do two distinct species whei:
crossed. This led me carefully to observe during four years many
seedlings, raised from several illegitimate unions. The chief result is

254 RECIPROCAL DIMORPHISM [Chap. IX

tliat these illegitimate plants, as they may be called, are not fully fer-
tile. It is possible to raise from dimorphic species, both long-styled
and short-styled illegitimate x:)laiits, and from trimorphic plants all
three illegitimate forms. These can then be properly united in a
legitimate manner. When this is done, there is no apparent reason
why they should not yield as many seeds as did their parents when
legitimately fertilised. But such is not the case. They are all
infertile, in various degrees ; some being so utterly and incurably
sterile that they did not yield during four seasons a single seed or
even seed-capsule. The sterility of these illegitimate plants, when
united with each other in a legitimate manner, may be strictly
compared with that of hybrids when crossed inter se. If, on the
other hand, a hybrid is crossed with either pure parent-species, the
sterility is usually much lessened : and so it is when an illegitimate
plant is fertilised by a legitimate plant. In the same manner ap
the steriUty of hybrids does not always run parallel with the
difEculty of making the first cross between the two parent-species,
so the sterility of certain illegitimate plants was unusually great,
whilst the sterility of the union from which they were derived was
by no means great. With hybrids raised from the same seed-
capsule the degree of sterility is innately variable, so it is in a
marked manner with illegitimate plants. Lastly, many hybrids are
profuse and persistent flowerers, whilst other and more sterile
hybrids produce few flowers, and are weak, miserable dwarfs;
exactly similar cases occur with the illegitimate offspring of various
dimorphic and trimorphic plants.

Altogether there is the closest identity in character and behaviour
between illegitimate plants and hybrids. It is hardly an exagge-
ration to maintain that illegitimate plants are hybrids, produced
within the limits of the same species by the improper imion ot
certain forms, whilst ordinary hybrids are produced from an im-
proper union between so-called distinct species. We have also
already seen that there is the closest similarity in all respects
between first illegitimate unions and first crosses between distinct
species. "l.'his will perhaps be made more fully apparent by an
illustration ; we may suppose that a botanist found two well-
marked varieties (and such occur) of the long-styled form of the
trimorphic Lythrum salicaria, and that he determined to try by
crossing whether they were specifically distinct. He would find
that they yielded only about one-fifth of the proper number of seed,
and that they behaved in all the other above specified respects as if
they had been two distinct species. But to make the case sure, he
would raise plants from his supposed hybridised seed, and he would

Chap. IX.] AND TPJMORPHISM. 255

find that the seedlings were miserably dwarfed and utterly sterik, and
that they behaved in all other respects like ordinary hybrids. He
might then maintain that he had actually proved, in accordance with
the common view, that his two varieties were as good and as distinct
species as any in the world ; but he would be completely mistaken.

The facts now given on dimorphic and trimorphic plants are
important, because they show us, first, that the physiological test
of lessened fertility, both in first crosses and in hybrids, is no safe
criterion of specific distinction ; secondly, because we may conclude
that there is some unknown bond which connects the infertility of
illegitimate unions with that of their illegitimate offspring, and we
are led to extend the same view to first crosses and hybrids ;
thirdly, because we find, and this seems to me of especial importance,
that two or three forms of the same species may exist and may
differ in no respect whatever, either in structure or in constitution,
relatively to external conditions, and yet be sterile when united in
certain ways. For we must remember that it is the union of the
sexual elements of individuals of the same form, for instance, of two
long-styled forms, which results in sterility ; whilst it is the union
of the sexual elements proper to two distinct forms which is fertile.
Hence the case appears at first sight exactly the reverse of what
occurs, in the ordinary unions of the individuals of the same species
and with crosses between distinct species. It is, however, doubtful
whether this is really so ; but I will not enlarge on this obscure
subject.

We may, however, infer as probable from the consideration of
dimorphic and trimorphic plants, that the sterility of distinct
species when crossed and of their hybrid progeny, depends exclu-
sively on the nature of their sexual elements, and not on any differ-
ence in their structure or general constitution. We are also led
to this same conclusion by considering reciprocal crosses, in which
the male of one species cannot be united, or can be united with
great difficulty, with the female of a second species, whilst the
converse cross can be effected with perfect facility. That excellent
observer, Gartner, likewise concluded that species when crossed are
sterile owing to differences confined to their reproductive systems.

Fertility of Varieties when Crossed, and of their Mongrel
Offspring, not universal.

It may be urged, as an overwhelming argument, that there must
be some essential distinction between species and varieties, inasmuch
as the latter, however much they may differ from each other in
QTitrrnal appearance* cross with perfect facility, and yield perfectly

256 FERTILITY OF VARIETIES WHEN CROSSED. [Chap. IX.

fertile offspring. With some exceptions, presently to be given, I
fully admit that this is the rule. But the subject is surrounded by
diflBculties, for, looking to varieties produced under nature, if two
forms hitherto reputed to be varieties be found in any degree sterile
together, they are at once ranked by most naturalists as species.
For instance, the blue and red pimpernel, which are considered by
most botanists as varieties, are said by Gartner to be quite sterile
when crossed, and he consequently ranks them as undoubted
species. If we thus argue in a circle, the fertility of all varieties
produced under nature will assuredly have to be granted.

If we turn to varieties, produced, or supposed to have been pro-
duced, under domestication, we are still involved in some doubt.
For when it is stated, for instance, that certain South American
indigenous domestic dogs do not readily unite with European dogs,
the explanation which will occur to every one, and probably the
true one, is that they are descended from aboriginally distinct
species. Nevertheless the perfect fertility of so many domestic
races, differing widely from each other in appearance, for instance
those of the pigeon, or of the cabbage, is a remarkable fact ; more
especially when we reflect how many species there are, which,
though resembling each other most closely, are utterly sterile when
intercrossed. Several considerations, however, render the fertility
of domestic varieties less remarkable. In the .first place, it may
be observed that the amount of external difference between two
species is no sure guide to their degree of mutual sterility, so that
similar differences in the case of varieties would be no sure guide.
It is certain that with species the cause lies exclusively in differ-
ences in their sexual constitution. Now the varying conditions
to which domesticated animals and cultivated plants have been
subjected, have had so little tendency towards modifying the
reproductive system in a manner leading to mutual sterility, that
we have good grounds for admitting the directly opposite doctrine
of Pallas, namely, that such conditions generally eliminate this
tendency ; so that the domesticated descendants of species, which in
their natural state probably would have been in some degree sterile
when crossed, become perfectly fertile together. With plants, so
far is cultivation from giving a tendency towards sterility between
distinct species, that in several well-authenticated cases already
alluded to, certain plants have been affected in an opposite manner,
for they have become self-impotent, whilst still retaining the
capacity of fertilising, and being fertilised by, other species. If
the Pallasian doctrine of the elimination of sterility through long-
3ontinued domestication be admitted, and it can hardly be rejecteii,

Ckap. IX.] FERTILITY OF VARIETIES WHEN CROSSED. 257

it becomes in the liighest degree improbable that similar conditions
long-continued should likewise induce this tendency; though in
certain cases, with species having a peculiar constitutioa, sterility
might occasionally be thus caused. Thus, as I believe, we can
understand why with domesticated animals varieties have not been
produced which are mutually sterile ; and why with plants only a
few such cases, immediately to be given, have been observed.

The real difficulty in our present subject is not, as it appears to
me, why domestic varieties have not become mutually infertile
when crossed, but why this has so generally occurred with naturla
varieties, as soon as they have been permanently modified in a
sufficient degree to take rank as species. We are far from precisely
knowing the cause ; nor is this surprising, seeing how profoundly
ignorant we are in regard to the normal and abnormal action of
the reproductive system. But we can see that species, owing to
their struggle for existence with numerous competitors, will have
been exposed during long periods of time to more uniform con-
ditions, than have domestic varieties ; and this may well make a
wide difference in the result. For we know how commonly wild
animals and plants, when taken from their natui-al conditions and
subjected to captivity, are rendered sterile ; and the reproductive
functions of organic beings which have always lived under natural
conditions would probably in like manner be eminently sensitive
to the influence of an unnatural cross. Domesticated productions,
on the other hand, which, as shown by the mere fact of their
domestication, were not originally highly sensitive to changes in
their conditions of life, and which can now generally resist with
undiminished fertility repeated changes of conditions, might be
expected to produce varieties, which would be little liable to have
their reproductive powers injuriously affected by the act of crossing
with other varieties which had originated in a like manner.

I have as yet spoken as if the varieties of the same species were
invariably fertile when intercrossed. But it is impossible to resist
the evidence of the existence of a certain amount of sterility in the
few following cases, which 1 will briefly abstract. The evidence is
at least as good as that from which we believe in the sterility of a
multitude of species. The evidence is, also, derived from hostile
witnesses, who in all other cases consider fertility and sterility as
s&fe criterions of specific distinction. Gartner kept during several
years a dwarf kind of maize with yellow seeds, and a tall variety
v/ith red seeds growing near each other in his garden ; and although
these plants have separated sexes, they never naturally crossed.
He then fertilised thirteen flowers of the one kind with poUec of the

258 FERTILITY OF VARIETIES WHEN CROSSED. [Chap. IX.

other; but only a single head produced any seed, and this one
head produced only five grains. Manipulation in this case could
not have been injurious, as the plants have separated sexes. No
one, I believe, has suspected that these varieties of maize are
distinct species; and it is important to notice that the hybrid
plants thus raised were themselves 'perfectly fertile ; so that even
Gartner did not venture to consider the two varieties as specifically
distinct.

Girou de Buzareingues crossed three varieties of gourd, which
like the maize has separated sexes, and he asserts that their mutual
fertilisation is hy so much the less easy as their differences are
greater. How far these experiments may be trusted, I know not ;
but the forms experimented on are ranked by Sageret, who mainly
founds his classification by the test of infertility, as varieties, and
jSTaudin has come to the same conclusion.

The following case is far more remarkable, and seems at first
incredible ; but it is the result of an astonishing number of experi-
ments made during many years on nine species of Verbascum, by
so good an observer and so hostile a witness as Gartner : namely
that the yellow and white varieties when crossed produce less seed
than the similarly coloured varieties of the same species. Moreover,
he asserts that, when yellow and white varieties of one species are
crossed with yellow and white varieties of a distinct species,
more seed is produced by the crosses between the similarly
coloured flowers, than between those which are differently coloured.
Mr. Scott also has experimented on the species and varieties ol
Verbascum ; and although unable to confirm Gartner's results on
the crossing of the distinct species, he finds that the dissimilarly
coloured varieties of the same species yield fewer seeds, in the pro-
|X)rtion of 86 to 100, than the similarly coloured varieties. Yet these
varieties differ in no respect except in the colour of their flowers ;
and one variety can sometimes be raised from the seed of another.

Kolreuter, whose accuracy has been confirmed by every subsequent
observer, has proved the remarkable fact, that one particular
variety of the common tobacco was mors fertile than the other
varieties, when crossed with a widely distinct species. He experi-
mented on five forms which are commonly reputed to be varieties,
and which he tested by the severest trial, namely, by reciprocal
crosses, and he found their mongrel offspring perfectly fertile. But
one of these five varieties, when used either as the father or mother
and crossed with the Nicotiana glutinosa, always yielded hybrids not
so sterile as those which were produced from the four other varieties
wbea GToesed with N. gl^ibinosa. Hence the reproductive system

CiiAP. IX.1 HYBRIDS AND MONGRELS COMPARED. 259

of this one variety must have "been in some manner and in some
degree modified.

]*'rom these facts it can no longer be maintained that varieties
when crossed are invariably quite fertile. From the great difficulty
of ascertaining the infertility of varieties in a state of nature, for
a supposed variety, if proved to be infertile in any degree, would
almost universally bo ranked as a species ; — from man attending
only to external characters in his domestic varieties, and from such
varieties not having been exposed for very long periods to uniform
conditions of Ufe ; — from these several considerations we may con-
clude that fertility does not constitute a fundamental distinction
between varieties and species when crossed. The general sterility
of crossed species may safely be looked at, not as a special acquire-
ment or endowment, but as incidental on changes of an unknown
nature in their sexual elements.

Hybrids and Mongrels compared, independently of their
fertility.

Independently of the question of fertility, the offspring of species
and of varieties when crossed may be compared in several other
respects. Gartner, whose strong wish it was to draw a distinct line
between species and varieties, could find very few, and, as it seems
to me, quite unimportant differences between the so-called hybrid
ofifsjjring of species, and the so-called mongrel offspring of varieties.
And, on the other hand, they agree most closely in many important
respects.

I shall here discuss this subject with extreme brevity. The most
important distinction is, that in the first generation mongrels are
more variable than hybrids ; but Gartner admits that hybrids from
species which have long been cultivated are often variable in the
first generation ; and I have myself seen striking instances of this
fact. Gartner further admits that hybrids between very closely
Jellied species are more variable than those from very distinct
species ; and this shows that the difference in the degree of varia-
bility graduates away. When mongrels and the more fertile hybrids
are propagated for several generations, an extreme amount of varia-
bility in the offspring in both cases is notorious ; but some few
instances of both hybrids and mongrels long retaining a uniform
character could be given. The variability, however, in the succes-
sive generations of mongrels is, perhaps, greater than in hybrids.

This greater variability in mongrels than in hybrids does not
Beem at all surprising. For the parents of mongrels are varieties,
and mostly domestic varistietj (very few experiments having been

B 2

260 HYBRIDS AND MONGRELS COMPARED. [Chap. IX.

tried on natural varieties), and this implies that there has beon
recent variability, which would often continue and would augment
that arising from the act of crossing. The slight variability of
hybrids in the first generation, in contrast with that in the succeed-
ing generations, is a curious fact and deserves attention. For ii
bears on the view which I have taken of one of the causes of
ordinary variability; namely, that the reproductive system from
being eminently sensitive to changed conditions of life, fails under
these circumstances to perform its proper function of producing
offspring closely similar in all respects to the parent-form. Now
hybrids in the first generation are descended from species (excluding
those long-cultivated) which have not had their reproductive
systems in any way affected, and they are not variable ; but
hybrids themselves have their reproductive systems seriously
affected, and their descendants are highly variable.

But to return to our comparison of mongrels and hybrids:
Glirtner states that mongrels are more liable than hybrids to revert
to either parent-form ; but this, if it be true, is certainly only a dif-
ference in degree. Moreover, Gartner expressly states that hybrids
from long cultivated plants are more subject to reversion thair
hybrids from species in their natural state ; and this probably
explains the singular difference in the results arrived at by different
observers : thus, Max Wicbura doubts whether hybrids ever revert
to their parent-forms, and ±ie experimented on uncultivated species
of willows; whilst Naudin, on the other hand, insists in the strongest
terms on the almost universal tendency to reversion in hybrids,
and he experimented chiefly on cultivated plants. Gartner further
states that when any two species, although most closely allied to
each other, are crossed with a third species, the hybrids are widely
different from each other ; whereas, if two very distinct varieties of
one species are crossed with another species, the hybrids do not
differ much. But this conclusion, as far as I can make out, is
founded on a single experiment ; and seems directly opposed to the
results of several experiments made by Kolreuter.

Buch alone are the unimportant differences which Gartner is able
to point out between hybrid and mongrel plants. On the other
hand, the degrees and kinds of resemblance in mongrels and in
hybrids to their respective parents, more especially in hybrids pro-
duced from nearly related species, follow according to Gartner the
same laws. When two species are crossed, one has sometimes a
prepotent power of impressing its likeness on the hybrid. So I
believe it to be with varieties of plants; and with animals one
variety certainly often has this prepotent power over another

<.'HAP. IX.] HYBRIDS AND MONGRELS COMPARED. 261

irariety. Hybrid plants pioduced from a reciprocal cross, generally
resemble each other closely ; and so it is with mongrel plants from
a reciprocal cross. Both hybrids and mongrels can be reduced tc
either pure parent-form, by repeated crosses in successive generations
with either parent.

These several remarks are apparently applicable to animals ; but
the subject is here much complicated, partly owing to the existence
of secondary sexual characters ; but more especially owing to pre-
potency in transmitting likeness running more strongly in one sex
than in the other, both when one species is crossed with another,
and when one variety is crossed with another variety. For instance,
[ think those authors are right, who maintain that the ass has a
prepotent power over the horse, so that both the mule and the hinny
resemble more closely the ass than the horse ; but that the pre-
potency runs more strongly in the male than in the female ass, so
that the mule, which is the oifspring of the male ass and mare, is
more like an ass, than is the hinny, which is the offspring of the
female-ass and stallion.

Much stress has been laid by some authors on the supposed fact,
that it is only with mongrels that the offspring are not intermediate
in character, but closely resemble one of their parents ; but this does
sometimes occur with hybrids, yet I grant much less frequently
than with mongrels. Looking to the cases which I have collected
of cross-bred animals closely resembling one parent, the resemblances
seem chiefly confined to characters almost monstrous in their nature,
and which have suddenly appeared — such as albinism, melanism,
■deficiency of tail or horns, or additional fingers and toes ; and do not
relate to characters which have been slowly acquired through selec-
tion. A tendency to sudden reversions to the perfect character of
cither parent would, also, be much more likely to occur with mongrels,
which are descended from varieties often suddenly produced and
semi-monstrous in character, than with hybrids, which are descended
from species slowly and naturally produced. On the whole, I
-entirely agree with Dr. Prosper Lucas, who, after arranging an
enormous body of facts with respect to animals, comes to the con-
clusion, that the laws of resemblance of the child to its parents are
the same, whether the two parents differ little or much from each
uther, namely, in the union of individuals of the same variety, or of
different varieties, or of distinct species.

Independently of the question of fertility and sterility, in all
other respects there seems to be a general and close similarity in
the offspring of crossed species, and of crossed varieties. If we
look at species as having been specially created, and at varieties as

262 SUMMARY. [Chap. JX.

having been produced by secondary laws, this similarity would be
an astonishing fact. But it harmonises perfectly with the view
that there is no essential distinction between species and varieties.

Summary of Chapter.

First crosses between forms, sufiSciently distinct to be ranked as
species, and their hybrids, are very generally, but not universally
sterile. The sterility is of all degrees, and is often so slight that the
most careful experimentalists have arrived at diametrically opposite
conclusions in ranking forms by this test. The sterility is innately
variable in individuals of the same species, and is eminently
susceptible to the action of favourable and unfavourable conditions.
The degree of sterility does not strictly follow systematic affinity,
but is governed by several curious and complex laws. It is generally
different, and sometimes widely different, in reciprocal crosses between
the same two species. It is not always equal in degree in a first
cross and in the hybrids produced from this cross.

In the same manner as in grafting trees, the capacity of one
species or variety to take on another, is incidental on Ufferences,
generally of an imknown nature, in their vegetative sysiems, so in
crossing, the greater or less facility of one species to unite with
another is incidental on unknown differences in their reproductive
systems. There is no more reason to think that species have been
specially endowed with various degrees of sterility to prevent their
crossing and blending in nature, than to think that trees have been
specially endowed with various and somewhat analogous degrees
of difficulty in being grafted together in order to prevent their
inarching in our forests.

The sterility of first crosses and of their hybrid progeny has not
been acquired through natural selection. In the case of first crosses
it seems to depend on several circumstances ; in some instances in
chief part on the early death of the embryo. In the case of hybrids,
it apparently depends on their whole organisation having been
disturbed by being compounded from two distinct forms ; the
sterility being closely allied to that which so frequently affects pure
species, when exposed to new and unnatural conditions of life,
tie who will explain these latter cases will be able to explain the
sterility of hybrids. This view is strongly supported by a parallelism
of another kind : namely, that, firstly, slight changes in the con-
ditions of life add to the vigour and fertility of all organic beings ;
and secondly, that the crossing of forms, which have been exposed -do
slightly difierent conditions of life or which have varied, favours the
size, vigour, and fertility of their offspring. The facts given on the

Chap. IX.] SUMMARY. 263

bterility OJ" the illegitimate unions of dimorphic and trimorphio
plants and of their illegitimate progeny, perhaps render it probable
that some unknown bond in all cases connects the degree of fertility
of first unions with that of their offspring. The consideration of these
facts on dimorphism, as well as of the results of reciprocal crosses,
clearly leads to the conclusion that the primary cause of the sterility
of crossed spo-cies is confined to differences in their sexual elements.
But why, in xhe case of distinct species, the sexual elements should
80 generally have become more or less modified, leading to their
mutual infertility, we do not know ; but it seems to stand in some
close relation to species having been exposed for long periods oi
time to nearly uniform conditions of life.

It is not surprising that the difficulty in crossing any two species,
and the sterility of their hybrid off'spring, should in most cases cor-
respond, even if due to distinct causes; for both depend on the
amount of difference between the species which are crossed. Nor
is it surprising that the facility of effecting a first cross, and the
fertihty of the hybrids thus produced, and the capacity of being
grafted together — though this latter capacity evidently depends on
widely different circumstances — should all run, to a certain extent,
parallel with the systematic affinity of the forms subjected to expe-
riment ; for systematic affinity includes resemblances of all kinds.

First crosses between forms known to be varieties, or sufficiently
alike to be considered as varieties, and their mongrel offspring, are
very generally, but not, as is so often stated, invariably fertile.
Nor is this almost universal and perfect fertility surprising, when
it is remembered how liable we are to argue in a circle with respect
to varieties in a state of nature ; and when we remember that the
greater number of varieties have been produced under domestication
by the selection of mere external differences, and that they have
not been long exposed to uniform conditions of life. It should also
be especially kep: in mind, that long-continued domestication tends
to eliminate sterility, and is therefore little likely to induce this
same quality. Independently of the question of fertility, in all
other respects there is the closest general resemblance between
hybrids and mongrels, — in their variability, in their power of
absorbing each other by repeated crosses, and in their inheritance
of characters from both parent-forms. Finally, then, although we
are as ignorant of the precise cause of the sterility of first crosses
and of hybrids as we are why animals and plants removed from
their natural conditions become sterile, yet the facts given in this
chapter do not seem to ine opposed to the belief that species
aborigirially existed as varieties.

State niS!'»nrHS dV^O

264 IMPERFECTION OF THE GEOLOGICAL RECORD. [Chap. X

CHAPTER X.

On the Imperfection of the Geological Eecord.

On the absence of intermediata varieties at the present day — On the nature
of extinct intermediate varieties; on their number — On the lapse ol
time, as 'inferred from the I'ate of denudation and of deposition — On
the lapse of time as estimated by years — On the poorness of our palaeon-
tological collections — On the intermittence of geological formations —
On the denudation of granitic areas — On the absence of intermediate
varieties in any one formation — On the sudden appearance of groups of
species — On their sudden a^ pearance in the lowest known fossiliferoiu
strata — Antiquity of the habitable earth.

In the sixth chapter I enumerated the chief objections which might
be justly urged against the views maintained in this volume.
Most of them have now been discussed. One, namely the dis-
tinctness of specific forms, and their not being blended together
by innumerable transitional links, is a very obvious difficulty.
I assigned reasons why such links do not commonly occur at the
present day under the circumstances apparently most favourable for
their presence, namely on an extensive and continuous area with
graduated physical conditions. I endeavoured to show, that the
life of each species depends in a more important manner on tho
presence of other already defined organic forms, than on climate
and, therefore, that the really governing conditions of life do not
graduate away quite insensibly like heat or moisture. I endea-
voured, also, to show that intermediate varieties, from existing in
lesser numbers than the forms which they connect, will generally
l>e beaten out and exterminated during the course of further modifi-
cation and improvement. The main cause, however, of innumerable
intermediate links not now occurring everywhere throughout nature,
depends on the very process of natural selection, through which new
varieties continually take the places of and supplant their parent-
t jrms. But just in proportion as this process of extermination has
BCted on an enormous scale, so must the number of intermediate
varieties, which have formerly existed, be truly enormous. Why
then is not every geological formation and every stratum full cf

LHAP. X.] IMPERFECTION OF THE GEOLOGICAL RECORD. 265

such intermediate links? Geology assuredly does not reveal any
Buch finely-graduated organic chain ; and this, perhaps, is the most
obvious and serious objection which can be urged against the theory.
The explanation lies, as I believe, in the extreme imperfection ol
the geological record.

In the first place, it should always be borne in mind what sort
of intermediate forms must, on the theory, have formerly existed.
I have found it difficult, when looking at any two species, to avoid
picturing to myself forms directly intermediate between them. But
this is a wholly false view ; we should always look for forms inter-
mediate between each species and a common but unknown pro-
genitor ; and the progenitor will generally have differed in some
respects from all its modified descendants. To give a simple
illustration : the fantail and pouter pigeons are both descended
from the rock-pigeon ; if we possessed all the intermediate varieties
which have ever existed, we should have an extremely close series
between both and the rock-pigeon ; but we should have no varieties
directly intermediate betw^een the fantail and pouter ; none, for
instance, combining a tail somewhat expanded with a crop some-
what enlarged, the characteristic features of these two breeds.
These two breeds, moreover, have become so much modified,
that, if we had no historical or indirect evidence regarding their
origin, it would not have been possible to liave determined, from a
mere comparison of their structure with that of the rock-pigeon,
C. livia, whether they had descended from this species or from some
other allied form, such as C. oenas.

So with natural species, if we look to forms very distinct, for
instance to the horse and tapir, we have no reason to suppose that
links directly interniediate between them ever existed, but between
each and an unknown common parent. The common parent will
have had in its whole organisation much general resemblance to the
tapir and to the horse ; but in some points of structure may have
differed considerably from both, even perhaps more than they
differ from each other. Hence, in all such cases, we should bo
unable to recognise the parent-form of any tw^o or more species,
even if we closely compared the structure of the parent with that of
its modified descendants, unless at the same time we had a nearly
perfect chain of the intermediate links.

It is just possible by the theory, that one of two living forma
might have descended from the other; for instance, a horse from a
tapir ; and in this case direct intermediate links will have existed
between them. But such a case would imply that one form had
remained for a very long period unaltered, whilst its descendantft

266 THE LAPSE OF TIME. [Chap. X.

had undergone a vast amount of change ; and the principle of com-
petition between organism and organism, between child and parent,
will render this a very rare event ; for in all cases the new and
improved forms of life tend to supplant the old and unimproved
forms.

By the theory of natural selection all living species have been
connected with the parent-species of each genus, by differences not
greater than we see between the natural and domestic varieties
of the same species at the present day ; and these parent-
species, now generally extinct, have in their turn been similarly
connected with more ancient forms ; and so on backwards, always
converging to the common ancestor of each great class. So that
the number of intermediate and transitional links, between all
living and extinct species, must have been inconceivably great. But
assuredly, if this theory be true, such have lived upon the earth.

On the Lajpse of Time, as inferred from the rate of Deposition and
extent of Denudation.

Independently of our not finding fossil remains of such infinitely
numerous connecting links, it may be objected that time cannot
have sufficed for so great an amount of organic change, all changes
having been effected slowly. It is hardly possible for me to
recall to the reader who is not a practical geologist, the facts
leading the mind feebly to comprehend the lapse of time. He
who can read Sir Charles Lyell's grand work on the Principles
of Geology, which the future historian will recognise as having pro-
duced a revolution in natural science, and yet does not admit how
vast have been the past periods of time, may at once close this
volume. Not that it suffices to study the Principles of Geology,
or to read special treatises by different observers on separate
formations, and to mark how each author attempts to give an
inadequate idea of the duration of each formation, or even of each
stratum. We can best gain some idea of past time by knowing
the agencies at work, and learning how deeply the surface of the
land lias been denuded, and how much sediment has been deposited.
As Lyell has well remarked, the extent and thickness of our sedi-
mentary formations are the result and the measure of the denu-
dation which the earth's crust has elsewhere undergone. Therefore
a man should examine for himself the great piles of superimposed
strata, and watch the rivulets bringing down mud, and the waves
wearing away the sea-cliffs, in order to comprehend something;
about the duration of past time, the monuments of which wc see
oil around us.

Chap. X.] THE LAPSE OF TIME. 267

It is good to wander along the coast, when formed of moderately
hard rocks, and mark the process of degradation. The tides in
most cases reach the cliffs only for a short time twice a day, and
the waves eat into them only when they are charged with sand or
pebbles ; for there is good evidence that pure water effects nothing
in wearing away rock. At last the base of the cliff is undermined,
huge fragments fall down, and these, remaining fixed, have to be
worn away atom by atom, until after being reduced in size they
can be rolled about by the waves, and then they are more quickly
2;round into pebbles, sand, or mud. But how often do we see along
the bases of retreating cliffs rounded boulders, all thickly clothed
by marine productions, showing how little they are abraded and
how seldom they are rolled about ! Moreover, if we follow for a
few miles any line of rocky cliff, which is undergoing degradation,
we find that it is only here and there, along a short length or
round a promontory, that the cliffs are at the present time suffering.
The appearance of the surface and the vegetation show that else-
where years have elapsed since the waters washed their base.

We have, however, recently learnt from the observations ot
Ramsay, in the van of many excellent observers — of Jukes, Geikie,
Croll, and others, that subaerial degradation is a much more im-
portant agency than coast-action, or the power of the waves. The
whole surface of the land is exposed to the chemical action of
the air and of the rain-water with its dissolved carbonic acid, and
in colder countries to frost ; the disintegrated matter is carried down
even gentle slopes during heavy rain, and to a greater extent than
might be supposed, especially in arid districts, by the wind; it
is then transported by the streams and rivers, which when rapid
deepen their channels, and triturate the fragments. On a rainy
day, even in a gently undulating country, we see the effects of
subaerial degradation in the muddy rills which flow down every
slope. Messrs. Eamsay and Whitaker have shown, and the ob-
servation is a most striking one, that the great lines of escarpment
in the Wealden district and those ranging across England, which
formerly were looked at as ancient sea-coasts, cannot have been
thus formed, for each line is composed of one and the same forma-
tion, whilst our sea-cliffs are everywhere formed by the intersection
of various formations. This being the case, we are compelled to
admit that the escarpments ewe their origin in chief part to the
rocks of which they are composed having resisted subaerial denu-
dation better than the surrounding surface ; this surface conse-
quently has been gradually lowered, with the lines of harder rock

26S THE LAPSE OF TIME. [Chap. X.

left projecting. Nothing impresses the mind with the vast duration
of time, according to our ideas of time, more forcibly than the con-
viction thus gained that subaerial agencies which apparently have
so little power, and which seem to work so slowly, have produced
great results.

When thus impressed with the slow rate at which the land is
worn away through subaerial and littoral action, it is good, in order
to appreciate the past duration of time, to consider, on the one hand,
the masses of rock which have been removed over many exten-
sive areas, and on the other hand the thickness of our sedimentary
formations. I remember having been much struck when viewing
volcanic islands, which have been worn by the waves and pared
all round into perpendicular cliffs of one or two thousand feet in
height ; for the gentle slope of the lava-streams, due to their for-
merly liquid state, showed at a glance how far the hard, rocky
beds had once extended into the open ocean. The same story is
told still more plainly by faults, — those great cracks along which
the strata have been upheaved on one side, or thrown down on
the other, to the height or depth of thousands of feet ; for since the
crust cracked, and it makes no great difference whether the up-
heaval was sudden, or, as most geologists now believe, was slow
and effected by many starts, the surface of the land has been so
completely planed down that no trace of these vast dislocations
is externally visible. The Craven fault, for instance, extends for
upwards of 30 miles, and along this line the vertical displacement
of the strata varies from 600 to 3000 feet. Professor Eamsay has
published an account of a downthrow in Anglesea of 2300 feet ;
and he informs me that he fully believes that there is one in Merio-
nethshire of 12,000 feet; yet in these cases there is nothing on
the surface of the land to show such prodigious movements; the
pile of rocks on either side of the crack having been smoothly swept
away.

On the other hand, in all parts of the world the piles of sedi-
mentary strata are of wonderful thickness. In the Cordillera I esti-
mated one mass of conglomerate at ten thousand feet ; and although
conglomerates have probably been accumulated at a quicker rate
than finer sediments, yet from being formed of worn and rounded
pebbles, each of which bears the stamp of time, they are good to
ehow how slowly the mass must have been heaped together. Pro-
fessor Ramsay has given me the maximum thickness, from actual
measurement in most cases, of the successive formations in dijfereril
parts of Great Britain ; and this is the result : —

Cha?. a.] the lapse of TIME. 269

Feet.
PalflBozoic strata (not including Igneous beds) .. .. 57,154

Secondary strata 13,190

Tertiary strata 2,240

— making altogcthsr 72,584 feet ; that is, very neaiiy ttirteen an^
three-quarters British miles. Some of the formations, which arc
represented in England by thin beds, are thousands of feet in
thickness on the Continent. Moreover, between each successive
formation, we have, in the opinion of most geologists, blank periods
of enormous length. So that tlie lofty pile of sedimentary rocks in
Britain gives but an inadequate idea of the time which has elapsed
during their accumulation. The consideration of these various facts
impresses the mind almost in the same manner as does the vain
endeavour to grapple with the idea of eternity.

Nevertheless this impression is partly false. Mr. Croll, in an
interesting paper, remarks that we do not err *' in forming too great
a conception of the length of geological periods," but in estimating
them by years. When geologists look at large and complicated
phenomena, and then at the figures representing several million
years, the two produce a totally different effect on the mind, and
the figures are at once pronounced too small. In regard to subaeria)
denudation, Mr. Croll shows, by calculating the known amount ol
sediment annually brought down by certain rivers, relatively to their
areas of drainage, that 1000 feet of solid rock, as it became gradu-
ally disintegrated, would thus be removed from the mean level of
the whole area in the course of six million years. This seems an
astonishing result, and some considerations lead to the suspicion
that it may be too large, but even if halved or quartered it is still
very surprising. Few of us, however, know what a million really
means : Mr. Croll gives the foUow^ing illustration : take a narrow
strip of paper, 83 feet 4 inches in length, and stretch it along the
wall of a large hall ; then mark off at one end the tenth of an inch.
This tenth of an inch will represent one hundred years, and the
entire strip a million years. But let it be borne in mind, in relation
to the subject of this work, what a hundred years implies, repre-
Bented as it is by a measure utterly insignificant in a hall of the
above dimensions. Several eminent breeders, during a single life-
time, have so largely modified some of the higher animals, which
propagate their kind much more slowly than most of the lower
animals, that they have formed what well deserves to be called a
new sub-breed. Few men have attended with due care to any one
strain for more than half a century, so that a hundred years repre-
sents the work of two breeders in suocessio" It is not to be pui>-

270 THE POORNESS OF OUR [Chap. X

posed that species in a state of nature ever change so quickly as
domestic animals under the guidance of methodical selection. The
comparison would be in every way fairer with the effects which
follow from unconscious selection, that is the preservation of the
most useful or beautiful animals, with no intention of modifying
the breed ; but by this process of unconscious selection, various
breeds have been sensibly changed in the course of two or three
centuries.

Species, however, probably change much more slowly, and within
the same country only a few change at the same time. This slow-
ness follows from all the inhabitants of the same country being
already so well adapted to each other, that new places in the polity
of nature do not occur until after long intervals, due to the occur-
rence of physical changes of some kind, or through the immigration
of new forms. Moreover variations or individual differences of the
right nature, by which some of the inhabitants might be better
fitted to their new places under the altered circumstances, would
not always occur at once. Unfortunately we have no means of
determining, according to the standard of years, how long a period
it takes to modify a species ; but to the subject of time we must
return.

On the Poorness of our Fnlceontological Collections.

Now let us turn to our richest geological museums, and what
a paltry display we behold ! That our collections are imperfect is
admitted by every one. The remark of that admirable palseonto-
logist, Edward Forbes, should never be forgotten, namely, that very
many fossil species are known and named from single and often
broken specimens, or from a few specimens collected on some one
spot. Only a small portion of the surface of the earth has been
geologically explored, and no part with sufiScient care, as the im-
portant discoveries made every year in Europe prove. No organism
wholly soft can be preserved. Shells and bones decay and disappear
when left on the bottom of the sea, where sediment is not accumu-
lating. We probably take a quite erroneous view, when we assume
that sediment is being deposited over nearly the whole bed of the
sea, at a rate sufficiently quick to embed and preserve fossil remains.
Throughout an enormously large proportion of the ocean, the bright
blue tint of the water bespeaks its purity. The many cases on
record of a formation conformably covered, after an immense
interval of time, by another and later formation, without the under-
lying bed having suffered in the interval any wear and tear, seem
explicable only on the view of the bottom of the sea not rarely lyin^

<r!HAP. X.] PALiEONTOLOGICAL COLLECTIONS. ' 271

for ages in an unaltered condition. The remains whicli do becx)me
embedded, if in sand or gravel, will, when the beds are upraised,
generally be dissolved by the percolation of rain-water charged with
carbonic acid. Some of the many kinds of animals which live on
the beach between high and low water mark seem to be rarely pre-
BeiTed. For instance, the several species of the Chthamalinse (a
sub-family of sessile cirripedes) coat the rocks all over the world in
infinite numbers : they ara all strictly littoral, with the exception
of a siogle Mediterranean species, which inhabits deep water, and
this has been found fossil in Sicily, whereas not one other species
has hitherto been found in any tertiary formation : yet it is known
that the genus Chthamalus existed during the Chalk period. Lastly,
many great deposits requiring a vast length of time for their accu-
mulation, are entirely destitute of organic remains, without our being
able to assign any reason : one of the most striking instances is
that of the Flysch formation, which consists of shale and sandstone,
several thousand, occasionally even six thousand feet, in thickness,
and extending for at least 300 miles from Vienna to Switzerland ;
and although this great mass has been most carefully Sf^arched, no
fossils, except a few vegetable remains, have been found.

With respect to the terrestrial productions which lived during
the Secondary and Palaeozoic periods, it is superfluous to state that
our evidence is fragmentary in an extreme degree. For instance,
until recently not a land shell was known belonging to either of
these vast periods, with the exception of one species discovered by
Sir C. Lyell and Dr. Dawson in the carboniferous strata of North
America; but now land-shells have been found in the lias. In
regard to mammiferous remains, a glance at the historical table
published in Lyell's Manual will bring home the tmth, how acci-
dental and rare is their preservation, far better than pages of detail.
Nor is their rarity surprising, when we remember how large a pro-
portion of the bones of tertiary mammals have been discovered
either in caves or in lacustrine deposits ; and that not a cave or true
lacustrine bed is known belonging to the age of our secondary or
palaeozoic formations.

But the imperfection in the geological record largely results
from another and more important cause than any of the foregoing ;
namely, from the several formations being separated from each
other by wide intervals of time. This doctrine has been empha-
tically admitted by many geologists and palasontologists, who, like
E. Forbes, entirely disbelieve in the change of species. When we
see the formations tabulated in written works, or when we follow
them in nature, it is difficult to avoid believing that they are closel j

272 THE POORNESS OF OUR [Chap. 1.

consecutive. But we know, for instance, from Sir R. Murchison*s
great work on Russia, what wide gaps there are in that country
between the superimposed formations ; so it is in North America,
and in many other parts of the world. The most skilful geologist,
if his attention had been confined exclusively to these large ter-
ritories, would never have suspected that, during the periods which
were blank and barren in his own country, great piles of sediment,
charged with new and peculiar forms of life, had elsewhere been
accumulated. And if, in each separate territory, hardly any idea
can be formed of the length of time which has elapsed between the
consecutive formations, we may infer that this could nowhere be
ascertained. The frequent and great changes in the mineralogical
composition of consecutive formations, generally implying great
changes in the geography of the surrounding lands, whence the
sediment was derived, accord with the belief of vast intervals of
time having elapsed between each formation.

We can, I think, see why the geological formations of each region
are almost invariably intermittent ; that is, have not followed each
other in close sequence. Scarcely any fact struck me more when
examining many hundred miles of the South American coasts, which
have been upraised several hundred feet within the recent period,
than the absence of any recent deposits sufficiently extensive to last
for even a short geological period. Along the whole west coast,
which is inhabited by a peculiar marine fauna, tertiary beds are so
poorly developed, that no record of several successive and peculiar
marine faunas will probably be preserved to a distant age. A little
reflection will explain why, along the rising coast of the western
side of South America, no extensive formations with recent or ter-
tiary remains can anywhere be found, though the supply of sediment
must for ages have been great, from the enormous degradation of
the coast-rocks and from muddy streams entering the sea. The
explanation, no doubt, is, that the littoral and sub-littoral deposits
are continually worn away, as soon as they are brought up by the
slow and gradual rising of the land within the grinding action of
the coast-waves.

We may, I think, conclude that sediment must be accumulated
in extremely thick, solid, or extensive masses, in order to. withstand
the incessant action of the waves, when first upraised and during
successive oscillations of level, as well as the subsequent subaerial
degradation. Such thick and extensive accumulations of sediment
may be formed in two ways ; either in profound depths of the sea,
in which case the bottom will not be inhabited by so many and
such varied forms of life, as the more shallow seas ; and the mass

Chap, X.] PAL^ONTOLOGICAL COLLECTIONS. 273

when upraised will give an imperfect record of the organisms whicb
existed in the neighbourhood during the period of its accumulation.
Or, Bediment may be deposited to any thickness and extent over a
shallow bottom, if it continue slowly to subside. In this latter case,
as long as the rate of subsidence and the supply of sediment nearly
balance each other, the sea will remain shallow and favourable for
many and varied forms, and thus a rich fossiliferous formation,
thick enough, when upraised, to resist a large amount of denudation,
may be formed.

I am convinced that nearly all our ancient formations, which are
throughout the greater part of their thickness rich in fossils, have
thus been formed during subsidence. Since publishing my view2
on this subject in 1845, 1 have watched the progress of Geology,
and have been surprised to note how author after author, in treat-
ing of this or that great formation, has come to the conclusion that
it was accumulated during subsidence. I may add, that the only
ancient tertiary formation on the west coast of South America,
which has been bulky enough to resist such degradation as it has
as yet suffered, but which will hardly last to a distant geological
age, was deposited during a downward oscillation of level, and thus
gained considerable thickness.

All geological facts tell ua plainly that each area has undergone
numerous slow oscillations of level, and apparently these oscillations
have affected wide spaces. Consequently, formations rich in fossils
and sufficiently thick and extensive to resist subsequent degradation
will have been formed over wide spaces during periods of subsidence,
but only where the supply of sediment was sufficient to keep the
sea shallow and to embed and preserve the remains before they had
time to decay. On the other hand, as long as the bed of the sea
remains stationary, thick deposits cannot have been accumulated
in the shallow parts, which are the most favourable to life. Still
less can this have happened during the alternate periods of elevation ;
or, to speak more accurately, the beds which were then accumulated
will generally have been destroyed by being upraised and brought
within the limits of the coast-action.

These remarks apply chiefly to littoral and sublittoral deposits.
In the case of an extensive aud shallow sea, such as that within a
large part of the Malay Archipelago, where the depth varies from
30 or 40 to 60 fathoms, a widely extended formation might be
fonned during a period of elevation, and yet not suffer excessively
from denudation during its slow upheaval ; but the thickness of tho
formation could not be great, for owing to the elevatory movement
it would be less than the depth in which it was formed ; nor would

274 DENUDATION OF GRANITIC AREAS. [Chap. X,

the deposit be much consolidated, nor be capped by ovei lying for-
mations, so that it would run a good chance of being worn away by
atmospheric degradation and by the action of the sea during sub-
sequent oscillations of level. It has, however, been suggested by
Mr. Hopkins, that if one part of the area, after rising and before
being denuded, subsided, the deposit formed during the rising move-
ment, though not thick, might afterwards become protected by fresh
accumulations, and thus be preserved for a long period.

Mr. Hopkins also expresses his belief that sedimentary beds of
considerable horizontal extent have rarely been completely destroyed.
But all geologists, excepting the few who believe that our present
metamorphic schists and plutonic rocks once formed the primordial
nucleus of the globe, will admit that these latter rocks have been
stript of their covering to an enormous extent. For it is scarcely
possible that such rocks could have been solidified and crystallized
whilst uncovered ; but if the metamorphic action occurred at pro-
found depths of the ocean, the former protecting mantle of rock
may not have been very thick. Admitting tben that gneiss, mica-
schist, granite, diorite, &c., were once necessarily covered up, how
can we account for the naked and extensive areas of such rocks in
many parts of the world, except on the belief that they have sub-
sequently boen completely denuded of all overlying strata ? That
such extensive areas do exist cannot be doubted : the granitic region
of Parime is described by Humboldt as being at least nineteen times
as large as Switzerland. South of the Amazon, Boue colours an
area composed of rocks of this nature as equal to that of Spain,
France, Italy, part of Germany, and the British Islands, all con-
joined. This region has not been carefully explored, but from the
concurrent testimony of travellers, the granitic area is very large :
thus. Von Eschwege gives a detailed section of these rocks,
stretching from Eio de Janeiro for 260 geographical miles inland in
a straight line ; and I travelled for 150 miles in another direction,
and saw nothing but granitic rocks. Numerous specimens, col-
lected along the whole coast from near Eio Janeiro to the mouth of
the Plata, a distance of 1100 geographical miles, were examined by
me, and they all belonged to this class. Inland, along the whole
northern bank of the Plata I saw, besides modern tertiary beds, only
one small patch of slightly metamorphosed rock, which alone could
have formed a part of the original capping of the granitic scries.
Turning to a well-known region, namely, to the United States and
Canada, as shown in Professor H. D. Rogers's beautiful map, I have
estimated the areas by cutting out and weighing the paper, and I
find that the metamorphic (excluding " the semi-metamorphic ")

Chap. X.] ABSENCE OF INTERMEDIATE VARIETIES. 275

and granitic rocks exceed, in the proportion of 19 to 12'5, the wliole
of the newer Pala307;oic formations. In many regions the metamor-
phic and granitic rocks would be fomid much more widely extended
than they appear to be, if all the sedimentary beds were removed which
rest unconformably on them, and which could not have formed part
of the original mantle under which they were crystallized. Hence
it is probable that in some parts of the world whole formations have
been completely denuded, with not a wreck left behind.

One remark is here worth a passing notice. During periods of
elevation the area of the land and of the adjoining shoal parts of the
sea will be increased, and new stations will often be formed ; — all
circumstances favourable, as previously explained, for the formation
of new varieties and species ; but during such periods there will
generally be a blank in the geological record. On the other hand,
during subsidence, the inhabited area and number of inhabitants
will decrease (excepting on the shores of a continent when first
broken up into an archipelago), and consequently during subsidence,
though there will be much extinction, few new varieties or species
will be formed ; and it is during these very periods of subsidence,
that the deposits which are richest in fossils have been accumulated.

On the Absence of Numerous Intermediate Varieties in any Single

Formation,

From these several considerations, it cannot be doubted that the
geological record, viewed as a whole, is extremely imperfect ; but if
we confine our attention to any one formation, it becomes much
more difiBcult to understand why we do not therein find closely
graduated varieties between the allied species which lived at its
commencement and at its close. Several cases are on record of the
same species presenting varieties in the upper and lower parts of
the same formation : thus, Trautschold gives a number of instances
with Ammonites ; and Hilgendorf has described a most curious case
of ten graduated forms of Planorbis multiformis in the successive
beds of a fresh-water formation in Switzerland. Although each
formation has indisputably required a vast number of years for its
deposition, several reasons can be given why each should not com-
monly include a graduated series of links between the species which
lived at its commencement and close; but I cannot assign due
proportional weight to the following considerations.

Although each formation may mark a very long lapse of -j ears,
each probably is short compared with the period requisite to change
one species into another. I am aware that two palaeontologists,
whose opinions are worthy of much deference, namely Bronn and

T 2

27C ABSENCE OF INTERMEDUTE VARIETIES [Chap. X.

Woodward, have concluded that the average duration of each for-
mation is twice or thrice as long as the average duration of specific
forms. But insuperable diflScultics, as it seems to me, prevent us
from coming to any just conclusion on this head. When we see a
species first appearing in the middle of any formation, it would be
rash in the extreme to infer that it had not elsewhere previously
existed. So again when we find a species disappearing before the
last layers have been deposited, it would be equally rash to suppose
that it then became extinct. We forget how small the area of
Europe is compared with the rest of the world ; nor have the
several stages of the same formation throughout Europe been cor-
related with perfect accuracy.

We may safely infer that with marine animals of all kinds there
has been a large amount of migration due to climatal and other
changes ; and when we see a species first appearing in any forma-
tion, the probability is that it only then first immigrated into that
area. It is well known, for instance, that several species appeared
somewhat earlier in the palaeozoic beds of North America than in
those of Europe ; time having apparently been required for their
migration from the American to the European seas. In examining
the latest deposits in various quarters of the world, it has every-
where been noted, that some few still existing species are common
in the deposit, but have become extinct in the immediately sur-
rounding sea ; or, conversely, that some are now abundant in the
neighbouring sea, but are rare or absent in this particular deposit.
It is an excellent lesson to reflect on the ascertained amount of
migration of the inhabitants of Europe during the glacial epoch,
which forms only a part of one whole geological period ; and like-
wise to reflect on the changes of level, on the extreme change of
climate, and on the great lapse of time, all included within this
same glacial period. Yet it may be doubted whether, in any
quarter of the world, sedimentary deposits, including fossil remains,
have gone on accumulating within the same area during the whole
of this period. It is not, for instance, probable that sediment was
deposited during the whole of the glacial period near the mouth of
the Mississippi, within that limit of depth at which marine animals
can best flourish: for we know that great geographical changes
occuiTcd in other parts of America during this space of time. When
\uch beds as were deposited in shallow water near the mouth of the
iilississippi during some part of the glacial period shall have been
upraised, organic remains will probably first appear and disappear
pt different levels, owing to the migrations of species and to geo-
graphical changes. And in the distant future, a geologist, examining

Chap. X.] IN ANY SINGLE FORMATION. 277

these beds, would be tempted to conclude that the average duration
of life of the embedded fossils had been less than that of the glacial
period, instead of having been really far greater, that is, extending
from before the glacial epoch to the present day.

In order to get a perfect gradation between two forms in the upper
and lower parts of the same formation, the deposit must have gone
on continuously accumulating during a long period, sufficient for
the slow process of modification ; hence the deposit must be a very
thick one ; and the species undergoing change must have lived in
the same district throughout the whole time. But we have seen
that a thick formation, fossiliferous throughout its entire thickness,
can accumulate only during a period of subsidence ; and to keep the
depth approximately the same, which is necessary that the same
marine species may live on the same space, the supply of sediment
must nearly counterbalance the amount of subsidence. But this
same movement of subsidence will tend to submerge the area
whence the sediment is derived, and thus diminish the supply,
whilst the downward movement continues. In fact, this nearly
exact balancing between the supply of sediment and the amount of
subsidence is probably a rare contingency ; for it has been observed
by more than one palaeontologist, that very thick deposits are
usually barren of organic remains, except near their upper or lower
limits.

It would seem that each separate formation, like the whole pile
of formations in any country, has generally been intermittent in its
accumulation. When we see, as is so often the case, a formation
composed of beds of widely different mineralogical composition, we
may reasonably suspect that the process of deposition has been
more or less interrupted. Nor will vhe closest inspection of a for-
mation give us any idea of the length of time which its deposition
may have consumed. Many instances could be given of beds only
a few feet in thickness, representing formations, which are else-
where thousands of feet in thickness, and which must have required
an enormous period for their accumulation ; yet no one ignorant of
this fact would have even suspected the vast lapse of time repre-
sented by the thinner formation. Many cases could be given of
the lower beds of a formation having been upraised, denuded, sub-
merged, and then re-covered by the upper beds of the same forma-
tion,— facts, show'ng what wide, yet easily overlooked, intervals
have occurred in its accumulation. In other cases we have the
plainest evidence in great fossilised trees, still standing upright as
they grew, of many long intervals of time and changes of level
during the process of deposition, which would not have been sue-

278 ABSENCE OF INTERMEPIATE VARIETIES [Chap. X

pected, had not the trees been preserved : thus Sir C. Lyell and
Dr. Dawson found carboniferous beds 1400 feet thick in Nova
Scotia, with ancient root-bearing strata, one above the other at no
less than sixty-eight different levels. Hence, when the same species
occurs at the bottom, middle, and top of a formation, the proba-
bility is that it has not lived on the same spot during the whole
period of deposition, but has disappeared and reappeared, perhaps
many times, during the same geological period. Consequently if it
were to undergo a considerable amount of modification during the
deposition of any one geological formation, a section would not in-
clude all the fine intermediate gradations which must on our theory
have existed, but abrupt, though perhaps slight, changes of form.

It is all-important to remember that naturalists have no golden
rule by which to distinguish species and varieties ; they grant
some little variability to each species, but when they meet with ?
somewhat greater amount of dilierence between any two forms,
they rank both as species, unless they are enabled to connect them
together by the closest intermediate gradations; and this, from
the reasons just assigned, we can seldom hope to effect in any one
geological section. Supposing B and C to be two species, and a
third, A, to be found in an older and underlying bed ; even if A
were strictly intermediate between B and C, it would simply be
ranked as a third and distinct species, unless at the same time it
could be closely connected by intermediate varieties with either one
or both forms. Nor should it be forgotten, as before explained,
that A might be the actual progenitor of B and C, and yet would
not necessarily be strictly intermediate between them in all respects.
So that we might obtain the parent-species and its several modified
descendants from the lower anei upper beds of the same formation,
and unless we obtained numerous transitional gradations, we should
aot recognise their blood-relationship, and should consequently rank
them as distinct species.

It is notorious on what excessively slight differences many palas-
oiitologists have founded their species ; and they do this the more
readily if the specimens come from different sub-stages of the same
formation. Some experienced conchologists are now sinking many
of the very fine species of D'Orbigny and others into the rank of
varieties; and on this view we do find the kind of evidence of
change which on the theory we ought to find. Look again at the
later tertiary deposits, which include many shells believed by the
majority of naturalists to be identical with existing species ; but
some excellent naturalists, as Agassiz and Pictet, maintain that ail
these tertiary species are specifically distinct, though the distincticn

Chap. X.] IN ANY SINGLE FORMATION. 279

is admitted to be very slight ; so that here, unless we believe that
these eminent naturalists have been misled by their imaginations,
and that these late tertiary species really present no difference what-
ever from their living representatives, or unless we admit, in oppo-
sition to the judgment of most naturalists, that these tertiary species
are all truly distinct from the recent, we have evidence of the fre-
quent occurrence of slight modifications of the kind required. If
we look to rather wider intervals of time, namely, to distinct but
consecutive stages of the same great formation, we find that the
embedded fossils, though universally ranked as specifically different,
yet are far more closely related to each other than are the species
found in more widely separated formations ; so that here again we
have undoubted evidence of change in the direction required by the
theory; but to this latter subject I shall return in the following
chapter.

With animals and plants that propagate rapidly and do not
wander much, there is reason to suspect, as we have formerly seen,
that their varieties are generally at first local ; and that such local
varieties do not spread widely and supplant their parent-forms until
they have been modified and perfected in some considerable degree.
According to this view, the chance of discovering in a formation in
any one country all the early stages of transition between any two
forms, is small, for the successive changes are supposed to have
been local or confined to some one spot. Most marine animals have
ii wide range ; and we have seen that with plants it is those which
have the widest range, that oftenest present varieties ; so that, with
shells and other marine animals, it is probable that those which
had the widest range, far exceeding the limits of the known geo-
logical formations of Europe, have oftenest given rise, first to local
varieties and ultimately to new species; and this again would
greatly lessen the chance of our being able to trace the stages of
transition in any one geological formation.

It is a more important consideration, leading to the same result,
as lately insisted on by Dr. Falconer, namely, that the period during
which each species underwent modification, though long as measured
by years, was probably short in comparison with that during which
it remained without undergoing any change.

It should not be forgotten, that at the present day, with perfect
specimens for examination, two forms can seldom be connected by
intermediate varieties, and thus proved to be the same species,
until many specimens are collected from many places; and with
fossil species this can rarely be done. We shall, perhaps, best per-
ceive th-3 improbability of our being enabled to connect species

280 ABSENCE OF INTERMEDIATE VARIETIES [Chap. X.

by numerous, fine, intermediate, fossil links, by asking ourselves
whether, for instance, geologists at some future period will be able
to prove that our different breeds of cattle, sheep, horses, and dogs
are descended from a single stock or from several aboriginal stocks ;
or, again, whetlicr certain sea-shells inhabiting the shores of North
America, which are ranked by some conchologists as distinct species
from their European representatives, and by other conchologists as
only varieties, are really varieties, or are, as it is called, specifically
distinct. This could be effected by the future geologist only by
his discovering in a fossil state numerous intermediate gradations ;
and such success is improbable in the highest degree.

It has been asserted over and over again, by writers who belie\'e
in the immutability of species, that geology yields no linking forms.
This assertion, as we shall see in the next chaptei, is certainly
erroneous. As Sir J. Lubbock has remarked, " Every species is a
link between other allied forms." If we take a genus having a score
of species, recent and extinct, and destroy four-fifths of them, no
one doubts that the remainder will stand much more distinct from
each other. If the extreme forms in the genus happen to have
been thus destroyed, the genus itself will stand more distinct from
other allied genera. What geological research has not revealed, is
the former existence of infinitel}'' numerous gradations, as fine as
existing varieties, connecting together nearly all existing and extinct
species. But this ought not to be expected ; yet this lias been
repeatedly advanced as a most serious objection against my views.

It may be worth while to sum up the foregoing remarks on the
causes of ^he imperfection of the geological record under an imagi-
nary illuF^ration. The Malay Archipelago is about the size of
Europe from the North Cape to the Mediterranean, and from Britain
to Eussia ; and therefore equals all the geological formations which
have been examined with any accuracy, excepting those of tho
United States of America. I fully agree with Mr. God win- Austen,
that the present condition of the Malay Archipelago, with its nume-
rous large islands separated by wide and shallow seas, probably
represents the former state of Europe, whilst most of our formations
were accumulating. The Malay Archipelago is one of the richest
regions in organic beings ; yet if all the species were to be collected
which have ever lived there, how imperfectly would they represent
the natural history of the world !

But we have every reason to believe that the terrestrial pro-
ductions of the archipelago would be preserved in an extremely
imperfect manner in the formations which we suppose to be thera
accumulating. Not many of the strictly littoral animals, or of

Chap. X.] IN ANY SINGLE FORMATION. 28,^

those which Uved oa naked submarine rocks, would be embedded ;
tind those embedded in gravel or sand would not endure to a distant
epoch. Wherever sediment did not accumulate on the bed of the
eea, or where it did not accumulate at a sufficient rate to protect
organic bodies from decay, no remains could be preserved.

Formations rich in fossils of many kinds, and of thickness
sufficient to last to an age as distant in futurity as the secondary
formations lie in the past, would generally be formed in the archi-
pelago only during periods of subsidence. These periods ot
subsidence would be separated from each other by immense inter-
vals of time, during which the area would be either stationary or
rising ; whilst rising, the fossiliferous formations on the steeper
shores would be destroyed, almost as soon as accumulated, by
the incessant coast-action, as we now see on the shores of Soiitli
America. Even throughout the extensive and shallow seas within
the archipelago, sedimentary beds could hardly be accumulated of
great thickness during the periods of elevation, or become capped
and protected by subsequent deposits, so as to have a good chance
of enduring to a very distant future. During the periods of sub-
sidence, there would probably be much extinction of life ; during
the periods of elevation, there would be much variation, but the
geological record would then be less perfect.

It may be doubted whether the duration of any one great period
of subsidence over the whole or part of the archipelago, together
with a contemporaneous accumulation of sediment, would exceed the
average duration of the same specific forms ; and these contingen-
cies are indispensable for the preservation of all the transitional
gradations between any two or more species. If such gradations
were not all fully preserved, transitional varieties would merely
appear as so many new, though closely allied species. It is also
probable that each great period of subsidence would be interrupted
by oscillations of level, and that slight climatal changes would inter-
vene during such lengthy periods ; and in these cases the inhabitants
of the archipelago would migrate, and no closely consecutive record
of their modifications could be preserved in any one formation.

Very many of the marine inhabitants of the archipelago now
i*ange thousands of miles beyond its confines ; and analogy plainly
leads to the belief that it would be chiefly these far-ranging species,
though only some of them, which would oftenest produce new
varieties ; and the vaneties would at first be local or confined
to one place, but if possessed of any decided advantage, or whes
further modified and improved, they would slowly spread and
supplant their parent-forms When such varieties returned t4i

282 SUDDEN APPEARANCE OF [Chap. X.

their ancient homes, as tliey would differ from their former state
in a nearly uniform, though perhaps extremely slight degree, and
as they would be found embedded in slightly different sub-stages of
tho same formation, they would, according to the principles followed
by many palaeontologists, be ranked as new and distinct species.

If then there be some degree of truth in these remarks, we have
no right to expect to find, in our geological formations, an infinite
number of those fine transitional forms which, on our theory, have
connected all the past and present species of the same group into
one long and branching chain of life. We ought only to look for a
few links, and such assuredly we do find — some more distantly,
some more closely, related to each other ; and these links, let them
be ever so close, if found in different stages of the same formation,
would, by many palaeontologists, be ranked as distinct species.
But I do not pretend that I should ever have suspected how poor
was the record in the best preserved geological sections, had not the
absence of innumerable transitional links between the species which
lived at the commencement and close of each formation, pressed so
hardly on my theory.

On the sudden Appearance of whole Groups of allied Species.

The abrupt manner in which whole groups of species suddenly
appear in certain formations, has been urged by several palaeontolo-
gists— for instance, by Agassiz, Pictet, and Sedgwick — as a fatal
objection to the belief in the transmutation of species. If numerous
species, belonging to the same genera or families, have really started
into life at once, the fact would be fatal to the theory of evolution
through natural selection. For the development by this means of
a group of forms, all of which are descended from some one progeni-
tor, must have been an extremely slow process ; and the progenitors
must have lived long before their modified descendants. But we
continually overrate the perfection of the geological record, and
falsely infer, because certain genera or families have not been found
beneath a certain stage, that they did not exist before that stage.
In ail cases positive palasontological evidence may be implicitly
trusted; negative evidence is worthless, as experience has so often
shown. We continually forget how large the world is, compared
with the area over which our geological formations have been
caref'iUy examined; we forget tliat groups of species m.ay else-
where have long existed, and have slowly multiplied, "before
they invaded the ancient archipeJagoes of Europe and the United
States. We do not make due allowance for the intervals of
time which have elapsed between our consecutive formations, —

Chap. X.] GROLTPS OF ALLIED SPECIES. 283

longer perhaps in many cases than the time required for the accu-
mulation of each formation. These intervals will have given time
for the multiplication of species from some one parent-form ; and in
the siiojeeding formation, such groups or species will appear as if
suddenly created.

I may here recall a remark formerly made, namely, that it might
require a long succession of ages to adapt an organism to some new
and peculiar line of life, for instance, to fly through the air ; and
consequently that the transitional forms would often long remain
confined to some one region ; but that, when this adaptation had
once been effected, and a few species had thus acquired a great
advantage over other organisms, a comparatively short time would
be necessary to produce many divergent forms, which would spread
rapidly and widely throughout the world. Professor Pictet, in his
excellent Review of this work, in commenting on early transitional
forms, and taking birds as an illustration, cannot see how the suc-
cessive modifications of the anterior limbs of a supposed prototype
could possibly have been of any advantage. But look at the
penguins of the Southern Ocean; have not th-ese birds their front
limbs in this precise intermediate state of " neither true arms nor
true wings"? Yet these birds hold their place victoriously in the
battle for life ; for they exist in infinite numbers and of many kinds.
I do not suppose that we here see the real transitional grades through
which the wings of birds have passed ; but what special difficulty is
there in believing that it might profit the modified descendants of
the penguin, first to become enabled to flap along the surface of the
sea like the logger-headed duck, and ultimately to rise from its
surface and glide through the air ?

I will now give a few examples to illustrate the foregoing remarks,
and to show how liable we are to error in supposing that whole
groups of species have suddenly been produced. Even in so short
an interval as that between the first and second editions of Pictet'a
great work on Palaeontology, published in 1844-46 and in 1853-57,
the conclusions on the first appearance and disappearance of several
groups of animals have been considerably modified ; and a third
edition would require still further changes. I may recall the well-
known fact that in geological treatises, published not many years
ago, mammals were always spoken of as having abruptly come in
at the commencement of the tertiary series. And now one of
the richest known accumulations of fossil mammals belongs to the
middle of the secondary series ; and true mammals have been dis-
covered in the new red sandstone at nearly the commencement of
this great series. Cuvier used to urge that no monkey occurred in

284 SUDDEN aPPEAKA.NCE OF [Cuap. X

any tertiary stratum ; but now extinct species have been discovered
in India, South America, and in Europe, as far back as the miocene
stage. Had it not been for the rare accident of the preservation of
footsteps in the new red sandstone of the United States, who would
have ventured to suppose that no less than at least thirty different
bird-like animals, some of gigantic size, existed during that period?
Not a fragment of bone has been discovered in these beds. Not long
ago, palasontologists maintained that the whole class of birds came
suddenly into existence during the eocene period ; but now we
know, on the authority of Professor Owen, that a bird certainly
lived during the deposition of the upper greensand ; and still more
recently, that strange bird, the Archeopteryx, with a long lizard-
like tail, bearing a pair of feathers on each joint, and with its wings
furnished with two free claws, has been discovered in the oolitic
slates of Solenhofen. Hardly any recent discovery shows more
forcibly than this, how little we as yet know of the former inhabi
tants of the world.

I may give another instance, which, from having passed under
my own eyes, has much struck me. In a memoir on Fossil Sessile
Cirripedes, I stated that, from the large number of existing and
extinct tertiary species ; from the extraordinary abundance of the
individuals of many species all over the world, from the Arctic
regions to the equator, inhabiting various zones of depths from the
Uj )per tidal limits to 50 fathoms ; from the perfect manner in which
specimens are preserved in the oldest tertiary beds ; from the case
with which even a fragment of a valve can be recognised ; from all
these circumstances, I inferred that, had sessile cirripedes existed
during the secondary periods, they would certainly have been pre-
served and discovered ; and as not one species had then been dis-
covered in beds of this age, I concluded that this great group had
been suddenly developed at the commencement of the tertiary series.
This was a sore trouble to me, adding as I then thought one more
instance of the abrupt appearance of a great group of species. But
my work had hardly been published, when a skilful palseontologist,
M. Bosquet, sent me a drawing of a perfect specimen of an unmis-
takeable sessile cirripede, which he had himself extracted from the
chalk of Belgium. And, as if to make the case as striking as
possible, this cirripede was a Chthamaius, a very common, large,
and ubiquitous genus, of which not one species has as yet been
found even in any tertiary stratum. Still more recently, a Pyrgoma,
a member of a distinct sub-family of sessile cirripedes, has been
discovered by Mr. Woodward in the upper chalk ; so that we now

Ckap. X.] GROUPS OF ALLIED SPECIES. 285

have abundant evidence of the existence of this group of animals
during the secondary period.

The case most frequently insisted on by palaeontologists of the
apparently sudden appearance of a whole group of species, is that of
the teleostean fishes, low down, according to Agassiz, in the Chalk
period. This group includes the large majority of existing species.
But certain Jurassic and Triassic forms are now commonly admitted
to be teleostean ; and even some palaeozoic forms have thus boen
classed by one high authority. If the teleosteans had really
appeared suddenly in the northern hemisphere at the commencement
of the chalk formation, the fact would have been highly remarkable;
but it would not have formed an insuperable difficulty, unless it
could likewise have been shown that at the same period the species
were suddenly and simultaneously developed in other quarters of
the world. It is almost superfluous to remark that hardly auy
fossil-fish are known from south of the equator ; and by running
through Pictet's Palaeontology it will be seen that very few species
are known from several formations in Europe. Some few families of
fish now have a confined range ; the teleostean fishes might formerly
have had a similarly confined range, and after having been largely
developed in some one sea, have spread widely. Nor have we
any right to suppose that the seas of the world have always been
so freely open from south to north as they are at present. Even at
this day, if the Malay Archipelago were converted into land, the
tropical parts of the Indian Ocean would form a large and perfectly
enclosed basin, in which any great group of marine animals might
be multiplied ; and here they would remain confined, until some of
the species became adapted to a cooler climate, and were enabled to
double the Southern capes of Africa or Australia, and thus reach
other and distant seas.

From these considerations, from our ignorance of the geology of
other countries beyond the confines of Europe and the United
States, and from the revolution in our paleeontological knowledge
effected by the discoveries of the last dozen years, it seems to me
to be about as rash to dogmatize on the succession of organic forms
thioughout the world, as it would be for a naturalist to land for five
minutes on a barren point in Australia, and then to discuss the
number and range of its productions.

On the sudden Appearance of Groups of allied Species in the
loivest known Fossiliferous Strata.

There is another and allied difficulty, which is much more serious.
I ailnde to the manner in which species belonging to several of the

286 GROUPS OF ALLIED SPECIES [Chap. X.

main divisions of the animal kingdom suddenly appear in tha
lowest known fossiliferous rocks. Most of the arguments which
have convinced me that all the existing species of the same group
are descended from a single progenitor, apply with equal force to
the earliest known species. For instance, it cannot be doubted that
all the Cambrian and Silurian trilobites are descended from some
one crustacean, which must have lived long before the Cambrian
age, and which probably differed greatly from any known animal.
Some of the most ancient animals, as the Nautilus, Lingula, &c., do
not differ much from living species ; and it cannot on our theory
be supposed, that these old species were the progenitors of all the
species belonging to the same groups which have subsequently
appeared, for they are not in any degree intermediate in character.

Consequently, if the theory be true, it is indisputable that before
the lowest Cambrian stratum was deposited, long periods elapsed, as
long as, or probably far longer than, the whole interval from the
Cambrian age to the present day ; and that during these vast
periods the world swarmed with living creatures. Here we en-
counter a formidable objection ; for it seems doubtful whether the
earth, in a fit state for the habitation of living creatures, has lasted
long enough. Sir W. Thompson concludes that the consolidation
of the crust can hardly have occuiTcd less than 20 or more than
400 million years ago, but probably not less than 98 or more
than 200 million years. These very wide limits show how doubt-
ful the data are ; and other elements may have hereafter to be
introduced into the problem. Mr. Croll estimates that about
60 million years have elapsed since the Cambrian period, but this,
judging from the small amount of organic change since the com-
mencement of the Glacial epoch, appears a very short time for the
many and great mutations of life, which have certainly occurred
since the Cambrian formation ; and the previous 140 million years
can hardly be considered as sufficient for the development of the
varied forms of life which already existed during the Cambrian
period. It is, however, probable, as Sir William Thompson insists,
that the world at a very early period was subjected to more rapid
and violent changes in its physical conditions than those now
occurring ; and such changes would have tended to induce changes
at a corresponding rate in the organisms which then existed.

To the question why we do not find rich fossiliferous deposits
belonging to these assumed earliest periods prior to the Cambrian
system, I can give no satisfactory answer. Several eminent geo-
logists, ^ith Sir E. Murchison at their head, were until recently
convinced that we beheld in the organic remains of the lowest

Chap. X.] IN LOWEST FOSSILIFEROUS STKATA. 287

Silurian stratum the first dawn of life. Other highly competent
judges, as Lyell and E. Forbes, have disputed this couclusion.
We should not forget that only a small portion of the world is
known with accuracy. Not very long ago M. Barrande added
another and lower stage, abounding with new and peculiar species,
beneath the then known Silurian system; and now, still lower
down in the Lower Cambrian formation, Mr. Hicks has found
in South Wales beds rich in trilobites, and containing various
molluscs and annelids. The presence of phosphatic nodules and
bituminous matter, even in some of the lowest azoic rocks, probably
indicates life at these periods ; and the existence of the Eozoon in
the Laurentian formation of Canada is generally admitted. Thera
are three great series of strata beneath the Silurian system in
Canada, in the lowest of which the Eozoon is found. Sir W.
Logan states that their " united thickness may possibly far surpass
" that of all the succeeding rocks, from the base of the palseozoic
" series to the present time. We are thus carried back to a period
" so remote, that the appearance of the so-called Primordial fauna
" (of Barrande) may by some be considered as a comparatively
" modern event." The Eozoon belongs to the most lowly organised
of all classes of animals, but is highly organised for its class ; it
existed in countless numbers, and, as Dr. Dawson has remarked,
certainly preyed on other minute organic beings, which must have
lived in great numbers. Thus the words, which I wrote in 1859,
about the existence of living beings long before the Cambrian
period, and which are almost the same with those since used by
Sir W. Logan, have proved true. Nevertheless, the difficulty of
assigning any good reason for the absence of vast piles of strata
rich in fossils beneath the Cambrian system is very great. It does
not seem probable that the most ancient beds have been quite
worn away by denudation, or that their fossils have been wholly
obliterated by metamorphic action, for if this had been the case
we should have found only small remnants of the formations next
succeeding them in age, and these would always have existed in a
partially metamorphosed condition. But the descriptions which we
possess of thCv-Silurian deposits over immense territories in Eussia
and in North America, do not support the view, that the older a
formation is, the more invariably it has suffered extreme denudation
and metamorphism.

The case at present must remain inexplicable ; and may be truly
urged as a valid argument against the views here entertained. To
show that it may hereafter receive some explanation, I will give
die following hypothesis. From the nature of the organic remai oa

288 GROUPS OF SPECIES IN LOWEST STRATA.. [Ciur. X.

Vv'hich do not appear to have inhabited profound depths, in the
several formations of Europe and of the United States ; and from
the amount of sediment, miles in thickness, of which the formations
are composed, we may infer that from first to last large islands
or tracts of land, whence the sediment was derived, occurred in the
neighbourhood of the now existing continents of Europe and
North America. This same view has since been maintained by
Agassiz and others. But we do not know what was the state
of things in the intervals between the several successive formations ;
whether Europe and the United States during these intervals
existed as dry land, or as a submarine surface near land, on which
sediment was not deposited, or as the bed of an open and unfathom-
able sea.

Looking to the existing oceans, which are thrice as extensive as
the land, we see them studded with many islands ; but hardly one
truly oceanic island (with the exception of New Zealand, if this
can be called a truly oceanic island) is as yet known to afford even
a remnant of any palreozoic or secondary formation. Hence we may
perhaps infer, that during the palaeozoic and secondary periods,
neither continents nor continental islands existed where our oceans
now extend ; for had they existed, palaeozoic and secondary forma-
tions would in all probability have been accumulated from sediment
derived from their wear and tear ; and these would have been at
least partially upheaved by the oscillations of level, which must
have intervened during these enormously long periods. If then we
may infer anything from these facts, we may infer that, where our
oceans now extend, oceans have extended from the remotest period
of which we have any record ; and on the other hand, that where
continents now exist, large tracts of land have existed, subjected no
doubt to great oscillations of level, since the Cambrian period. The
coloured map appended to my volume on Coral Reefs, led me to
conclude that the great oceans are still mainly areas of subsidence,
the great archipelagoes still areas of oscillations of level, and the
continents areas of elevation. But we have no reason to assume
that things have thus remained from the beginning of the world.
Our continents seem to have been formed by a preponderance, during
many oscillations of level, of the force of elevation ; but may not
the areas of preponderant movement have changed in the lapse of
ages ? At a period long antecedent to the Cambrian epoch, con-
1 kients may have existed where oceans are now spread out ; and
^lear and open oceans may have existed where our continents now
siand. Nor should we be justified in assuming that if, for instance
tuc bed of the Pacific Ocean were now converted into a continent

Chap. >:.] IMPERFECTION OF GEOLOGICAL RECORD. 289

we should there find sedimentary formations in a recognisable
condition older than the CamLrian strata, supposing such to have
been formerly deposited ; for it might well happen that strata
which had g'ibsided some milea nearer to the centre of the earth,
and which had been pressed on by an enormous weight of superin-
cumbent water, might have undergone far more metamorphic action
than strata which have always remained nearer to the surface.
The immense areas in some parts of the world, for instance in
South America, of naked metamorphic rocks, which must have been
heated under great pressure, have always seemed to me to require
some special explanation ; and we may perhaps believe that we see
in these large areas, the many formations long anterior to the
Cambrian epoch in a completely metamorphosed and denuded
condition.

The several difficulties here discussed, namely — that, though we
find in our geological formations many links betwe-en the species
which now exist and which formerly existed, we do not find
infinitely numerous fine transitional forms closely joining them all
together ; — the sudden manner in which several groups of species
first appear in our European formations ; — the almost entire absence,
as at present known, of formations rich in fossils beneath the
Cambrian strata, — are all undoubtedly of the most serious nature.
We see this in the fact that the most eminent paleeontologists,
namely, Cuvier, Agassiz, Barrande, Pictet, Falconer, E. Forbes, &c.,
and ail our greatest geologists, as Lyell, Murchison, Sedgwick,
&c., have unanimously, often vehemently, maintained the immu-
tability of species. But Sir Charles Lyell now gives the support of
his high authority to the opposite side ; and most geologists and
palaeontologists are much shaken in their former belief. Those
Avho believe that the geological record is in any degree perfect, will
undoubtedly at once reject the theory. For my part, following out
Lyell's metaphor,!! look at the geological record as a history of the
world imperfectly kept, and written in a changing dialect; of this
history we possess the last volume alone, relating only to two or
three countries. Of this volume, only here and there a short
chapter has been preserved ; and of each page, only here and there
a few lines. Each word of the slowly-changing language, more or
less different in the successive chapters, may represent the forms of
life, which are entombed in our consecutive formations, and which
falsely appear to us to have been abruptly introduced. On this
view, the difficulties above discussed are greatly diminished, or even
disapjjear.

u

29C THE GEOLOGICAL SUCCESSIOX [Chap. XL

CHAPTEK XL

On the Geological Succession of Organic Beings.

On the slow and successive appearance of new species — On their differeiit
rates of change — Species once lost do not reappear — Groups of species
follow the same general rules in their appearance and disappearance as
do single species — On extinction — On simultaneous changes in the
forms of life throughout the world — On the affinities of extinct species
to each other and to living species — On the state of development of
ancient forms — On the succession of the same types within the same
areas — Summary of preceding and present chapter.

Let us now see w],ietlier the several facts and laws relating to the
geological succession of organic beings accord best with the common
view of the immutability of species, or with that of their slow and
gradual modification, through variation and natural selection.

New species have appeared very slowly, one after another, both
on the land and in the waters. Lyell has shown that it is hardly
possible to resist the evidence on this head in the case ol the several
tertiary stages ; and every year tends to fill up the blanks between
the stages, and to make the proportion between the lost and exist-
ing forms more gradual. In some of the most recent beds, though
undoubtedly of high antiquity if measured by years, only one or
two species are extinct, and only one or two are new, having
appeared there for the first time, either locally, or, as far as we
know, on the face of the earth. The secondary formations are
more broken ; but, as Bronn has remarked, neither the appearance
nor disappearance of the many species embedded in each formation
has been simultaneous.

Species belonging to different genera and classes have not changed
at the same rate, or in the same degree. In the older tertiary
beds a few living shells may still be found in the midst of a mul-
titude of extinct forms. Falconer has given a striking instance
of a similar fact, for an existing crocodile is associated with many
losu mammals and reptiles in the sub-Himalayan deposits. The
Silurian Lingula differs but little from the living species of this
genus ; whereas most of the other Silurian Molluscs and all the
Crustaceans have changed greatly. The productions of the land

Chap. XI.J OF ORGANIC BEINGS. 291

seem to have changed at a quicker rate than those of the sea, of
which a striking instance has been observed in Switzerland. There
is some reason to believe that organisms high in the scale, change
more quickly than those that are low : though there are exceptions
to this rule. The amount of organic change, as Pictet has remarked,
is not the same in each successive so-called formation. Yet if we
compare any but the most closely related formations, all the species
will be found to have undergone some change. When a species
has once disappeared from the face of the earth, we have no reason to
believe that the same identical form ever reappears. The strongest
apparent exception to this latter rule is that of the so-called
" colonies " of M. Barrande, which intrude for a period in the midst of
an older formation, and then allow the pre-existing fauna to reappear ;
but Lyell's explanation, namely, that it is a case of temporary
migration from a distinct geographical province, seems satisfactory.
These several facts accord well with our theory, which includea
no fixed law of development, causing all the inhabitants of an area
to change abruptly, or simultaneously, or to an equal degree. The
process of modification must be slow, and will generally affect only
a few species at the same time ; for the variability of each species
is independent of that of all others. Whether such variations or
individual differences as may arise will be accumulated through
natural selection in a greater or less degree, thus causing a greater
or less amount of permanent modification, will depend on many
complex contingencies — on the variations being of a beneficial
nature, on the freedom of intercrossing, on the slowly changing
physical conditions of the country, on the immigration of new
colonists, and on the nature of the other inhabitants with which
the varying species come into competition. Hence it is by no
means surprising that one species should retain the same identical
form much longer than others ; or, if changing, should change in a
less degree. We find similar relations between the existing inha-
bitants of distinct countries; for instance, the land-shells and
coleopterous insects of Madeira have come to differ considerably
from their nearest allies on the continent of Europe, whereas the
marine shells and birds have remained unaltered. We can perhaps
understand the apparently quicker rate of change in terrestrial
and in more highly organised productions compared with marine
and lower productions, by the more complex relations of the higher
beings to their organic and inorganic conditions of life, as explained
in a fonner chapter. When many of the inhabitants of any area
have l^ecome modified and improved, we can understand, on the
principle of competition, anri from the all-important relations of

u 2

292 THE GEOLOGICAL SUCCESSION [Chap. XI.

organism to organism in the struggle for life, that any form which
did not become in some degree modified and improved, would be
liable to extermination. Hence we see why all the species in the
same region do at last, if we look to long enough intervals of time,
become modified, for otherwise they would become extinct.

In members of the same class the average amount of change,
during long and equal periods of time, may, perhaps, be nearly the
same; but as the accumulation of enduring formations, rich in
/^ToSsils, depends on great masses of sediment being deposited oq
; subsiding areas, our formations have been almost necessarily accu-
mulated at wide and irregularly intermittent intervals of time ;
consequently the amount of organic change exhibited by the fossils
embedded in consecutive formations is not equal. Each formation^
on this view, does not mark a new and complete act of creation,
but only an occasional scene, taken almost at hazard^^ an ever
slowly changing_dram3,- t "^

We can clearly understand why a species when once lost should
never reappear, even if the very same conditions of life, organic and
inorganic, phould recur. For though the offspring of one species
might be adapted (and no doubt this has occurred in innumerable
instances) to fill the place of another species in the economy of
nature, and thus supplant it ; yet the two forms — the old and the
new — would not be identically the same ; for both would almost
certainly inherit different characters from their distinct progenitors ;
and organisms already differing would vary in a different manner.
For instance, it is possible, if all our fantail pigeons were destroyed,
that fanciers might make a new breed hardly distinguishable from
the present breed ; but if the parent rock-pigeon were likewise
destroyed, and under nature we have every reason to believe that
parent-forms are generally supplanted and exterminated by their
improved offspring, it is incredible that a fantail, identical with the
existing breed, could be raised from any other species of pigeon, or
even from any other well-established race of the domestic pigeon,
for the successive variations would almost certainly be in some
degree different, and the newly-formed variety would probably
inherit from its progenitor some characteristic differences.

Groups of species, that is, genera and families, follow the same
general rules in their appearance and disappearance as do single
species, changing more or less quickly, and in a greater or lesser
degree. A group, when it has once disappeared, never reappears ;
that is, its existence, as long as it lasts, is continuous. I am
aware that there are some apparent exceptions to this rule, but the
exceptions are surprisingly few, so few that E. Forbes, Pictet, and

Chaf. XI ] OF ORGANIC BEINGS. 293

Woodw ard (though all strongly opposed to such views as I maintain)
admit it^ truth ; and the rule strictly accords with the theory. For
all the sj^ecies of the same group, however long it may have lasted,
are the modified descendants, one from the other, and all from a
common progenitor. In the genus Lingula, for instance, the species "
which have successively appeared at all ages must have been con-
nected by an unbroken series of generations, from the lowest

Silurian stratum to the present day.

7We~liave seen in the last chapter that whole groups of species
sbmetimes falsely appear to have been abruptly developed ; and ]
I have attempted to give an explanation of this fact, which if true— >
mmld be fatal to my views. But such cases are certainly excei)-
tional ; the general rule being a gradual increase in number, until
the group reaches its maximum, and then, sooner or later, a gradual
decrease. If the number of the species included within a genus,
or the number of the genera within a family, be represented by a
vertical line of varying thickness, ascending through the successive
geological formations in which the species are found, the line will
sometimes falsely appear to begin at its lower end, not in a sharp
point, but abruptly ; it then gradually thickens upwards, often
keeping of equal thickness for a space, and ultimately thins out in
the upper beds, marking the decrease and final extinction of the
species. This gradual increase in number of the species of a group
is strictly conformable with the theory, for the species of the same
genus, and the genera of the same family, can increase only slowly
and progressively ; the process of modification and the production
of a number of allied forms necessarily being a slow and gradual
process, — one species first giving rise to two or three varieties, these
being slowly converted into species, which in their turn produce by
equally slow steps other varieties and species, and so on, like the
branching of a great tree from a single stem, till the group becomes
targe.

On Extinction.

We have as yet spoken only incidentally of the disappearance of
Jspecies and of groups of species. On the theory of natural selection,
the extinction of old forms and the production of new and improved
forms are intimately connected together. The old notion of all the
inhabitants of the earth having been swept away by catastrophes
at successive periods is very generally given up, even by those
geologists, as Elie de Beaumont, Murchison, Barrande, &c., whose
general views would n&turally lead them to this conclusion. On
the contraiy, we have every reason to believe, from the study of the

State Hibl"?,^:.-

294 EXTINCTION. [Chap. XL

tertiary formations, that species and groups of species gradually
disappear, one after another, first from one spot, then from another,
and finally from the world. In some few cases, however, as by the
breaking of an isthmus and the consequent irruption of a multitude
of new inhabitants into an adjoining sea, or by the final subsidence
of an island, the process of extinction may have been rapid. Both
single species and whole groups of species last for very unequal
periods; some groups, as we have seen, have endured from the
earliest known dawn of life to the present day ; some have dis-
appeared before the close of the palaeozoic period. No fixed law
seems to determine the length of time during which any single
species or any single genus endures. There is reason to believe that
the extinction of a whole group of species is generally a slower pro-
cess than their production : if their appearance and disappearance-
be represented, as before, by a vertical line of varying thickness
tlie line is found to taper more gradually at its upper end, which
marks the progress of extermination, than at its lower end, which
marks the first appearance and the early increase in number of the
species. In some cases, however, the extermination of whole
groups, as of ammonites, towards the close of the secondary period,
has been wonderfully sudden.

The extinction of species has been involved in the most gratuitous'
mystery. Some authors have even supposed that, as the individual
has a definite length of life, so have species a definite duration. No-
one can have marvelled more than I have done at the extinction of
species. When I found in La Plata the tooth of a horse embedded
with the remains of Mastodon, Megatherium, Toxodon, and other
extinct monsters, which all co-existed with still living shells at a
very late geological period, I was filled with astonishment; for^
seeing that the horse, since its introduction by the Spaniards into
South America, has run wild over the whole country and has
increased in numbers at an unparalleled rate, I asked myself what
could so recently have exterminated the former horse under con-
ditions of life apparently so favourable. But my astonishment was
groundless. Professor Owen soon perceived that the tooth, though
so like that of the existing horse, belonged to an extinct species.
Had this horse been still living, but in some degree rare, no naturalist
would have felt the least surprise at its rarity ; for rarity is the
attribute of a vast number of species of all classes, in all countries.
If we ask ourselves why this or that species is rare, we answer-
that something is unfavourable in its conditions of life ; but what
that something is, we can hardly ever tell. On the supposition of
the fossil horse still existing as a rare species, we might have felt

Chap. XI.J EXTINCTION, iiS5

certain, from the analogy of all other mammals, even of the slow-
breeding elephant, and from the history of the natm*alisation of the
domestic horse in South America, that under more favourable con-
ditions ir, would in a very few years have stocked the whole
continent. But we could not have told what the unfavourable con-
ditions were which checked its increase, whether some one or several
contingencies, and at what period of the horse's life, and in what
degree, they severally acted. If the conditions had gone on, how-
ever slowly, becoming less and less favourable, we assuredly should
not have perceived the fact, yet the fossil horse would certainly
have become rarer and rarer, and finally extinct ; — its place being
seized on by some more successful competitor.

It is most difficult always to remember that the increase of every
creature is constantly being checked by unperceived hostile agencies j
and that these same unperceived agencies are amply sufficient to
cause rarity, and finally extinction. So little is this subject under-
stood, that I have heard surprise repeatedl}^ expressed at such great
monsters as the Mastodon and the more ancient Dinosaurians having
become extinct; as if mere bodily strength gave victory in the
battle of life. Mere size, on the contrary, would in some cases
determine, as has been remarked by Owen, quicker extermination
from the greater amount of requisite food. Before man inhabited
India or Africa, some cause must have checked the continued
increase of the existing elephant. A highly capable judge. Dr.
Falconer, believes that it is chiefly insects which, from incessantly
harassing and weakening the elephant in India, check its increase ;
and this was Bruce's conclusion with respect to the African elephant
in Abyssinia. It is certain that insects and blood-sucking bats
determine the existence of the larger naturalised quadrupeds ia
several parts of S. America.

We see in many cases in the more recent tertiar}^ formations,
that rarity precedes extinction ; and we know that this has been
the progress of events with those animals which have been exter-
minated, either locally or wholly, through man's agency. I may
repeat what I published in 1845, namely, that to admit that species
generally become rare before they become extinct — to feel no sur-
prise at the rarity of a species, and yet to marvel greatly when the
species ceases to exist, is much the same as to admit that sickness
in the individual is the forerunner of death — to feel no surprise
at sickness, but, when the sick man dies, to wonder and to suspect
that he died by some deed of violence.

The theory of natural selection is grounded on the belief that
each new variety and ultimately each new species, is produced and

296 EXTINCTION. [Chap. XI.

maintained by having some advantage over those with which it
comes into competition ; and the consequent extinction of the less-
favoured forms ahuost inevitably follows. It is the same with our
domestic productions ; when a new and slightly improved variety
has been raised, it at first supplants the less improved varieties in
the same neighbourhood ; when much improved it is transported
far and near, like our short-horn cattle, and takes the place of other
breeds in other countries. Thus the appearance of new forms and
the disappearance of old forms, both those naturally and those arti-
ficially produced, are bound together. In flourishing groups, the
number of new specific forms which have been produced within a
given time has at some periods probably been greater than the
number of the old specific forms which have been exterminated ;
but we know that species have not gone on indefinitely increasing,
at least during the later geological epochs, so that, looking to later
times, we may believe that the production of new forms has caused
the extinction of about the same number of old forms.

The competition will generally be most severe, as formerly ex-
plained and illustrated by examples, between the forms which are
most like each other in all respects. Hence the improved and
modified descendants of a species will generally cause the extermi-
nation of the parent-species ; and if many new forms have been
developed from any one species, the nearest allies of that species,
i.e. the species of the same genus, will be the most liable to extermi-
nation. Thus, as I believe, a number of new species descended
from one species, that is a new genus, comes to supplant an old
genus, belonging to the same family. But it must often have
happened that a new species belonging to some one group has seized
on the place occupied by a species belonging to a distinct group,
and thus have caused its extermination. If many allied forms be
developed from the successful intruder, many will have to yield
their places ; and it will generally be the allied forms, which will
suffer from some inherited inferiority in common. But whether it
be species belonging to the same or to a distinct class, which have
yielded their places to other modified and improved species, a few
of the sufferers may often be preserved for a long time, from being
fitted to some peculiar line of life, or from inhabiting some distant
and isolated station, where they will have escaped severe competi-
tion. For instance, some species of Trigonia, a great genus of shells
in the secondary formations, survive in the Australian seas ; and a few
members of the great and almost extinct group of Ganoid fishes still
inhabit our fresh waters. Therefore the utter extinction of a group
is generally, as we have seen, a slower process than its production.

Chap. XL] EXTINCTION. 297

With respect to the apparently sudden externTiination of whole
families or orders, as cf Trilobites at the close of the palaeozoic
period and of Ammonites at the close of the secondary period, we
mnst remember what has been already said on the probable wide
intervals of time between our consecutive formations ; and in these
intervals there may have been much slow extermination. More-
over, when, by sudden immigration or by unusually rapid develop-
ment, many species of a new group have taken possession of an
area, many of the older species will have been exterminated in a
correspondingly rapid manner; and the forms which thus yield
their places will commonly be allied, for they will partake of the
same inferiority in common.

Thus, as it seems to me, the manner in which single species and
whole groups of species become extinct accords well with the theory
of natural selection. We need not marvel at extinction ; if we
must marvel, let it be at our own presumption in imagining for a
moment that we understand the many complex contingencies on
which the existence of each species depends. If we forget for an
instant, that each species tends to increase inordinately, and that
some check is always in action, yet seldom perceived by us, the
whole economy of nature will be utterly obscured. Whenever we
can precisely say why this species is more abundant in individuals
than that ; why this species and not another can be naturalised in
a given country ; then, and not until then, we may justly feel sur-
prise why we cannot account for the extinction of any particulai
species or group of species.

On the Forms of Life changing almost simultaneously throughout

the World.

Scarcely any palseontological discovery is more striking than the
fact, that the forms of life change almost simultaneously throughout
tk'C world. Thus our European Chalk formation can be recognised
in many distant regions, under the most different climates, where
not a fragment of the mineral chalk itself can be found ; namely,
in North America, in equatorial South America, in ^J'ierra del
Fuego, at the Cape of Good Hope, and in the peninsula of India.
For at these distant points, the organic remains in certain beds pre-
sent an unmistakeable resemblance to those of the Chalk. It is
not that the same species are met with ; for in some cases not one
species is identically the same, but they bekng to the same fami-
lies, genera, and sections of genera, and sometimes are similarly
characterised in such trifling points as mere superficial sculpture.
Moreover, otlier forms, which are not found in the Chalk of Europe

298 FORMS OF LIFE CHANGING [Chap. XI

but whiich occur in the formations either above or below, (xjcur in
the same order at these distant points of the world. In the several
successive palaeozoic formations of Eussia, Western Europe, and
North America, a similar parallelism in the forms of life has been
observed by several authors : so it i.s, according to Lyell, with the
European and North American tertiary deposits. Even if the few
lossil species which are common to the Old and New Worlds were
kept wholly out of view, the general parallelism in the successive
forms of life, in the palaeozoic and tertiary stages, would still be
manifest, and the several formations could be easily correlated.

These observations, however, relate to the marine inhabitants of
the world : we have not sufficient data to judge whether the pro-
ductions of the land and of fresh water at distant points change in
the same parallel manner. We may doubt whether they have thus
changed : if the Megatherium, Mylodon, Macrauchenia, and Toxo-
don had been brought to Europe from La Plata, without any in-
formation in regard to their geological position, no one would have
suspected that they had co-existed with sea-shells all still living ;
but as these anomalous monsters co-existed with the Mastodon and
Horse, it might at least have been inferred that they had lived
during one of the later tertiary stages.

When the marine forms of life are spoken of as having changed
simultaneously throughout the world, it must not be supposed that
this expression relates to the same year, or to the same century >
or even that it has a very strict geological sense ; for if all the
marine animals now living in Europe, and all those that lived
in Europe during the pleistocene period (a very remote period as
measured by years, including the whole glacial epoch) were com-
pared with those now existing in South America or in Australia,
the most skilful naturalist would hardly be able to say whether
the present or the pleistocene inhabitants of Europe resembled most
closely those of the southern hemisphere. So, again, several highly
competent observers maintain that the existing productions of the
United States are more closely related to those which lived in
Europe during certain late tertiary stages, than to the present
inhabitants of Europe ; and if this be so, it is evident that fossili-
ferous beds now deposited on the shores of North America would
hereafter be liable to be classed with somewhat older European
beds. Nevertheless, looking to a remotely future epoch, there can
be little doubt that all the more modern raarine formations, namely,,
the upper pliocene, the pleistocene and strictly modern beds, of
Europe, North and South America, and Australia, from containing:
fossil remains in some degree allied, and from not including those

Chap. XI.] THROUGHOUT THE WORLD. 299

forms which are found only in the older underlying deposits, would
he correctly ranked as simultaneous in a geological sense.

The fact of the forms of life changing simultaneously, in the
above large sense, at distant parts of the world, has greatly struck
those admirable observers, MM. de Verneuil and d'Archiac. After
referring to the parallelism of the palasozoic forms of life in various
parts of Europe, they add, " If, struck by this strange sequence, we
" turn our attention to North America, and there discover a series
" of analogous phenomena, it will appear certain that all these modi-
" fications of species, their extinction, and the introduction of new
" ones, cannot be owing to mere changes in marine currents or other
"causes more or less local and temporary, but depend on genera.
" laws which govern the whole animal kingdom." M. Barrando
has made forcible remarks to precisely the same effect. It is, indeed,
quite futile to look to changes of currents, climate, or other physical
conditions, as the cause of these great mutations in the forms of life
throughout the world, under the most different climates. We must,
as Barrande has remarked, look to some special law. We shall see
this more clearly when we treat of the present distribution of organic
beings, and find how slight is the relation between the physical
conditions of various countries and the nature of their inhabitants.

This great fact of the parallel succession of the fonns of life
throughout the world, is explicable on the theory of natural selec-
tion. New species are formed by having some advantage over
older forms ; and the forms, which are already dominant, or have
some advantage over the other forms in their own country, give
birth to the greatest number of new varieties or incipient species.
We have distinct evidence on this head, in the plants which are
dominant, that is, which are commonest and most widely diflused,
producing the greatest number of new varieties. It is also natural
that the dominant, varying, and far-spreading species, which have
already invaded to a certain extent the territories of other species,
should be those which would have the best chance of spreading still
further, and of giving rise in new countries to other new varieties
and species. The process of diffusion would often be very slow,
depending on climatal and geographical changes, on strange acci-
dents, and on the gradual acclimatisation of new species to the
various climates through which they might have to pass, but in
the course of time the dominant forms would generally succeed in
spreading and would ultimately prevail. The diffusion would, it k
probable, be slower with the terrestrial inhabitants of distinct con
linents than with the marine inhabitants of the continuous sea.
We might therefore expect to find, as we do find, a less strict degree

300 FORMS OF LIFE CHANGING. PChap. XI.

of parallelism in the succession of the productions of the land than
with those of the sea.

Thus, as it seems to me, the parallel, and, taken in a large sense,
simultaneous, succesi^ion of the same forms of life throughout the
world, accords well \vith the principle of new species having been
formed by dominant species spreading widely and varying ; the new
species thus produced being themselves dominant, owing to their
having had some advantage over their already dominant parents, as
well as over other species, and again spreading, varying, and j)ro-
ducing new forms. The old forms which are beaten and which
yield their places to the new and victorious forms, will generally'' bt
allied in groups, from inheriting some inferiority in common ; and
therefore, as new and improved groups spread throughout the world,
old groups disappear from the world ; and the succession of form?
everywhere tends to correspond both in their first appearance and
final disappearance.

There is one other remark connected with this subject worth
making. I have given my reasons for believing that most of our
great formations, rich in fossils, were deposited during periods of
subsidence ; and that blank intervals of vast duration, as far as
fossils are concerned, occurred during the periods when the bed of
the sea was either stationary or rising, and likewise when sediment
was not thrown down quickly enough to embed and pi-eserve organic
remains. During these long and blank intervals I suppose that the
inhabitants of each region underwent a considerable amount of
modification and extinction, and that there was much migration
from other parts of the world. As we have reason to believe that
large areas are affected by the same movement, it is probable that
strictly contemporaneous formations have often been accumulated
over very wide spaces in the same quarter of the world ; but we are
very far from having any right to conclude that this has invariably
been the case, and that large areas have invariably been affected by
the same movements. When two formations have been deposited
in two regions during nearly, but not exactly, the same period, we
should find in both, from the causes explained in the foregoing
paragraphs, the same general succession in the forms of life ; but
the species would not exactly correspond ; fcr there will have been
a little more time in the one region than in the other for modifica-
tion, extinction, and immigration.

I suspect that cases of this nature occur in Europe. Mr.
Prestwich, in his admirable Memoirs on the eocene deposits of
England and France, is able to draw a close general parallelism
between the successive stages in the two countries; but when be

CHAP. XI.] AFFINITIES OF EXTINCT SPECIES. 301

compares certain stages in England with those in France, although
he finds in both a curious accordance in the numbers of the species
belonging to the same genera, yet the species themselves differ in
a manner very difficult to account for considering the proximity
of the two areas, — unless, indeed, it be assumed that an isthmus
separated two seas inhabited by distinct, but contemporaneous,
faunas. Lyell has made similar observations on some of the later
tertiary formations. Barrande, also, shows that there is a striking
general parellelism in the successive Silurian deposits of Bohemia
and Scandinavia ; nevertheless he finds a surprising amount of
difference in the species. If the several formations in these regions
have not been deposited during the same exact periods, — a forma-
tion in one region often corresponding with a blank interval in the
other, — and if in both regions the species have gone on slowly
changing during the accumulation of the several formations and
during the long intervals of time between them ; in this case the
several formations in the two regions could be arranged in the same
order, in accordance with the general succession of the forms of life,
and the order would falsely appear to be strictly parallel ; never-
theless the species would not be all the same in the apparently
corresponding stages in the two regions.

On the AJJinities of Extinct Species to each other, and to Living

Forms.

Let us now look to the mutual affinities of extinct and living
species. All fall into a few grand classes ; and this fact is at once
explained on the principle of descent. The more ancient any form
is, the more, as a general rule, it differs from living forms. But,
as Buckland long ago remarked, extinct species can all be classed
either in still existing groups, or between them. That the extinct
forms of life help to fill up the intervals between existing genera,
families, and orders, is certainly true ; but as this statement has
often been ignored or even denied, it may be well to make some
remarks on this subject, and to give some instances. If we confine
our attention either to the living or to the extinct species of the
same class, the series is far less perfect than if we combine both into
Dne general system. In the writings of Professor Owen we continually
meet with the expression of generalised forms, as applied to extinct
animals ; and in the writings of Agassiz, of prophetic or synthetic
types; and these terms imply that such forms are in fact inter-
mediate or connecting linl^s. Another distinguished palaeontologist,
M. Gaudty, has shown in the most striking manner that many of
the fossil mammals discovered by him in Attica serve to break

i502 AFFINITIES OF EXTINCT SPECIES. [Chap. Xi

down the intervals between existing genera. Cuvier ranked tiie
Euminants and Pachyderms, as two of the most distinct orders of
mammals ; but so many fossil links have been disentombed that
Owen has had to alter the whole classification, and has placed
certain pachyderms in the same sub-order with ruminants ; for
example, he dissolves by gradations the apparently wide interval
between the pig and the camel. The Ungulata or hoofed quad-
rupeds are now divided into the even-toed or odd-toed divisions;
but the Macrauchenia of S. America connects to a certain extent
these two grand divisions. No one will deny that the Hipparion is
intermediate between the existing horse and certain older ungulate
forms. What a wonderful connecting link in the chain of mammals
is the Typotherium from S. America, as the name given to it by
Professor Gervais expresses, and which cannot be placed in any
existing order. The Sirenia form a very distinct group of mammals,
and one of the most remarkable peculiarities in the existing dugong
and lamentin is the entire absence of hind limbs, without even a
rudiment being left ; but the extinct Halitherium had, according
to Professor Flower, an ossified thigh-bone " articulated to a well-
defined acetabulum in the pelvis," and it thus makes some approach
to ordinary hoofed quadrupeds, to which the Sirenia are in other
respects allied. The cetaceans or whales are widely different from
all other mammals, but the tertiary Zeuglodon and Squalodon,
which have been placed by some naturalists in an order by them-
selves, are considered by Professor Huxley to be undoubtedly ceta-
ceans, " and to constitute connecting links with the aquatic car-
nivora."

Even the wide interval between birds and reptiles has been
shown by the naturalist just quoted to be partially bridged over in
the most unexpected manner, on the one hand, by the ostrich and
extinct Archeopteryx, and on the other hand, by the Compso-
gnathus, one of the Dinosaurians — that group which includes the
most gigantic of all terrestrial reptiles. Turning to the Inverte-
brata, Barrande asserts, and a higher authority could not be named,
that he is every day taught that, although paleozoic animals can
certainly be classed under existing groups, yet that at this ancient
period the groups were not so distinctly separated from each other
as they now are.

Some writers have objected to any extinct species, or group of
species, being considered as intermediate between any two living
species, or groups of species. If by this term it is meant that
an extinct form is directly intermediate in all its characters be-
tween two living forms or groups, the objection is probably valid

CHiJP. XL] AFFINITIES OF EXTINCT SPECIES. 303

But in a natural classification many fossil species certainly stand
between living species, and some extinct genera between living
genera, even between genera belonging to distinct families. The
most common case, especially with respect to very distinct groups,
such as fish and reptiles, seems to be, that, supposing them to be
distinguished at the present day by a score of characters, the ancient
members are separated by a somewhat lesser number of characters ;
so that the two groups formerly made a somewhat nearer approach
to each other than they now do.

It is a common belief that the more ancient a form is, by so
much the more it tends to connect by some of its characters groups
now widely separated from each other. This remark no doubt
must be restricted to those groups which have undergone much
change in the course of geological ages ; and it would be difficult
to prove the truth of the proposition, for every now and then even
a living animal, as the Lepidosiren, is discovered having affinities
directed towards very distinct groups. Yet if we compare the
older Eeptiles and Batrachians, the older Fish, the older Cepha-
lopods, and the eocene Mammals, with the more recent members
of the same classes, we must admit that there is truth in the
remark.

Let us see how far these several facts and inferences accord with
the theory of descent with modification. As the subject is some-
what complex, I must request the reader to turn to the diagram
in the fourth chapter. We may suppose that the numbered letters
in italics represent genera, and the dotted lines diverging from
ihem the species in each genus. The diagram is much too simple,
too few genera and too few species being given, but this is un-
important for us. The horizontal lines may represent successive
geological formations, and all the forms beneath the uppermost
line may be considered as extinct. The three existing genera
a", <2^*, j:)^^ will form a small family; ?>" and/" a closely allied
family or sub-family ; and o^*, e", m^^, a third family. These
three families, together with the many extinct genera on the
several lines of descent diverging from the parent-form (A) will
form an order ; for all will have inherited something in common
from their ancient progenitor. On the principle of the continued
tendency to divergence of character, which was formerly illus-
trated by this diagram, the more recent any form is, the more
it will generally difier from its ancient progenitor. Hence we
can understand the rule that the most ancient fossils differ most
from existing forms. We must not, however, assume that diver-
gence of character is a necessary contingency ; it depends solely

304 AFFINITIES Ot EXTINCT SPECIES. [Chap. XI

on the descendants from a species being thus enabled to seize on
many and different places in the economy of nature. Therefore it
is quite possible, as we have seen in the case of some Silurian forms,
that a species might go on being slightly modified in relation to
its slightly altered conditions of life, and yet retain throughout a
vast period the same general characteristics. This is represented
in the diagram by the letter f".

All the many forms, extinct and recent, descended frcm (A),
make, as before remarked, one order; and this order, from the
continued effects of extinction and divergence of character, has
become divided into several sub-families and families, some of
which are supposed to have perished at different periods, and some
to have endured to the present day.

By looking at the diagram we can see that if many cf the extinct
forms supposed to be imbedded in the successive formations, were
discovered at several points low down in the series, the three
existing families on the uppermost line would be rendered less
distinct from each other. If, for instance, the genera a^, a^, a^^,
/■*, m^, m^, m^, were disinterred, these three families would be so
closely linked together that they probably would have to be united
into one great family, in nearly the same manner as has occurred
with ruminants and certain pachyderms. Yet he who objected to
consider as intermediate the extinct genera, which thus link together
the living genera of three families, would be partly justified, for
they are intermediate, not directly, but only by a long and cir-
cuitous course through many widely different forms. If many
extinct forms were to be discovered above one of the middle
horizontal lines or geological formations — for instance, above
No. VI. — but none from beneath this line, then only two of
the families (those on the left hand, a^*, &c., and h^*, &c.) would
have to be united into one ; and there would remain two families,
which would be less distinct from each other than they were
before the discovery of the fossils. So agam if the three families
formed of eight genera (a^* to m^*), on the uppermost line, be
supposed to differ from each other by half-a-dozen important
characters, then the families which existed at the period marked
YI. would certainly have differed from each other by a less number
of characters ; for they would at this early stage of descent have
diverged in a less degree from their common progenitor. Thus it
comes that ancient and extinct genera are often in a greater or less
degree intermediate in character between their modified descendants,
or between their collateral relations.

Under nature the process will be far more complicated than is

Chap. XI.] AFFINITIES OF EXTINCT SPECIES. 305

represented in the diagram; for the groups will have been raore
numerous ; they will have endured for extremely unequal lengths
of time, and will have been modified in various degrees. As we
possess only the last volume of the geological record, and that in
a very broken condition, we have no right to expect, except
in rare cases, to fill up the wide intervals in the natural system,
and thus to unite distinct families or orders. All that we have
a right to expect is, that those groups which have, within known
geological periods, undergone much modification, should in the
older formations make some slight approach to each other ; so
that the older members should differ less from each ' other in
some of their characters than do the existing members of the
same groups; and this by the concurrent evidence of our best
paheontologists is frequently the case.

Thus, on the theory of descent with modification, the main facts
with respect to the mutual affinities of the extinct forms of life
to each other and to living forms, are explained in a satisfactory
manner. And they are wholly inexplicable on any other view.

On this same theory, it is evident that the fauna during any
one great period in the earth's history will be intermediate in
general character between that which preceded and that which
succeeded it. Thus the species which lived at the sixth great
stage of descent in the diagram are the modified offspring of those
which lived at the fifth stage, and are the parents of those which
"became still more modified at the seventh stage ; hence they could
hardly fail to be nearly intermediate in character between the forms
of life above and below. We must, however, allow for the entire
extinction of some preceding forms, and in any one region for the
immigration of new forms from other regions, and for a large
amount of modification during the long and blank intervals between
the successive formations. Subject to these allowances, the fauna
of each geological period undoubtedly is intermediate in character*,
between the preceding and succeeding faunas. I need give only
one instance, namely, the manner in which the fossils of the
Devonian system, when this system was first discovered, were at
once recognised by palaeontologists as intermediate in character
between those of the overlying carboniferous, and underlying
Silurian systems. But each fauna is not necessarily exactly inter-
mediate, as unequal intervals of time have elapsed between con*-
sccutive formations.

It is no real objection to the truth of the statement that the
fauna of each period as a whole is nearly intermediate in character
between the preceding and succeeding faunas, that certain genera

306 AFFINITIES OF EXTINCT SPECIES. [Chap. XI^

ofifer exceptions to the rule. For instance, the species of mastodons
and elephants, when arranged by Dr. Falconer in two series, — in
the first place according to their mutual affinities, and in the second
place according to their periods of existence, — do not accord in
arrangement. The species extreme in character are not the oldest
or the most recent ; nor are those which are intermediate in cha-
racter, intermediate in age. But supposing for an instant, in this
and other such cases, that the record of the first appearance and
disappearance of the species was complete, which is far from the
case, we have no reason to believe that forms successively produced
necessarily endure for coiTesponding lengths of time. A very
ancient form may occasionally have lasted much longer than a form
elsewhere subsequently produced, especially in the case of terres-
trial productions inhabiting separated districts. To compare small
things with great ; if the principal living and extinct races of the
domestic pigeon were arranged in serial affinity, this arrangement
would not closely accord with the order in time of their production,
and even less with the order of their disappearance ; for the parent
rock-pigeon still lives ; and many varieties between the rock-pigeon
and the carrier have become extinct; and carriers which are
extreme in the important character of length of beak originated
earlier than short-beaked tumblers, which are at the opposite end
of the series in this respect.

Closely connected with the statement, that the organic remains
from an intermediate formation are in some degree intermediate
in character, is the fact, insisted on by all palaeontologists, that
fossils from two consecutive formations are far more closely related
to each other, than are the fossils from two remote formations.
Pictet gives as a well-known instance, the general resemblance of
the organic remains from the several stages of the Chalk forma-
tion, though the species are distinct in each stage. This fact alone,
from its generality, seems to have shaken Professor Pictet in
his belief in the immutability of species. He who is acquainted
with the distribution of existing species over the globe, will not
attempt to account for the close resemblance of distinct species in
closely consecutive formations, by the physical conditions of the
ancient areas having remained nearly the same. Let it be remem-
bered that the forms of life, at least those inhabiting the sea, have
changed almost simultaneously throughout the world, and there-
fore under the most different climates and conditions. Consider
the prodigious vicissitudes of climate during the pleistocene period,
which includes the whole glacial epoch, and note how little the
epecific forms of the inhabitants of the sea have been affected.

CttAP. XL] STATE OF DEVELOPMENT. 307

On the theory of descent, the full meaning of the fossil remains
from closely consecutive formations being closely related, though
ranked as distinct species, is obvious. As the accumulation of each
formation has often been interrupted, and as long blank intervals
have intervened between successive formations, we ought not to
expect to find, as I attempted to show in the last chapter, in any
one or in any two formations, all the intermediate varieties between
the species which appeared at the commencement and close of these
periods : but we ought to find after intervals, very long as measured
by years, but only moderately long as measured geologically,
closely allied forms, or, as they have been called by some authors,
representative species ; and these assuredly we do find. We find,
in short, such evidence of the slow and scarcely sensible mutation?
of specific forms, as we have the right to expect.

On the State of Develojpment of Ancient compared with Living

Forms.

We have seen in the fourth chapter that the degree of differentia-
tion and specialisation of the parts in organic beings, when arrived
at maturity, is the best standard, as yet suggested, of their degree
of perfection or highness. We have also seen that, as the speciali-
sation of parts is an advantage to each being, so natural selection
will tend to render the organisation of each being more specialised
and perfect, and in this sense higher ; not but that it may leave
many creatures with simple and unimproved structures fitted for
simple conditions of life, and in some cases will even degrade or
simplify the organisation, yet leaving such degraded beings better
fitted for their new walks of life. In another and more general
manner, new species become superior to their predecessors ; for they
have to beat in the struggle for life all the older forms, with which
they come into close competition. We may therefore' conclude
that if under a nearly similar climate the eocene inhabitants of the
world could be put into competition with the existing inhabitants,
the former would be beaten and exterminated by the latter, as
would the secondary by the eocene, and the pala3ozoic by the
secondary forms. So that by this fundamental test of victory in
the battle for life, as well as by the standard of the specialisation of
organs, modern forms ought, on the theory of natural selection, to
stand higher than ancient forms. Is this the case? A large
majority of palaeontologists would answer in the affirmative ; and it
seems that this answer must be admitted as true, though difiicult of
proof.

It is no valid objection ' o this conclusion, that certain Brachiopcds

X 2

308 STATE OF DEVELOPMENT OK [Chap. XL

have been but slightly modified from an extremely remote geological
epoch ; and that certain land and fresh-water shells have remained
nearly the same, from the time when, as far as is known, they first
appeared. It is not an insuperable difiiculty that Foraminifera have
not, as insisted on by Dr. Carpenter, progressed in organisation since
even the Laurentian epoch ; for some organisms would have to
remain fitted for simple conditions of life, and what could be better
fitted for this end than these lowly organised Protozoa ? Such
objections as the above would be fatal to my view, if it included
advance in organisation as a necessary contingent. They would
likewise be fatal, if the above Foraminifera, for instance, could be
proved to have first come into existence during the Laurentian
epoch, or the above Brachiopods during the Cambrian formation ; for
in this case, there would not have been time sufficient for thu
development of these organisms up to the standard which they
had then reached. When advanced up to any given point, there is
no necessity, on the theory of natural selection, for their further
continued progress ; though they will, during each successive age,
have to be slightly modified, so as to hold their places in relation to
slight changes in their conditions. The foregoing objections hinge
on the question whether we really know how old the world is, and
at what period the various forms of life first appeared; and this
may well be disputed.

The problem whether organisation on the whole has advanced is
in many ways excessively intricate. The geological record, at all
times imperfect, does not extend far enough back, to show with
unmistakeable clearness that within the known history of the world
organisation has largely advanced Even at the present day, looking
to members of the same class, naturalists are not unanimous which
forms ought to be ranked as highest : thus, some look at the
selaceans or sharks, from their approach in some important points
of structure to reptiles, as the highest fish ; others look at the
teleosteans as the highest. The ganoids stand intermediate between
the selaceans and teleosteans ; the latter at the present day are
largely preponderant in number ; but formerly selaceans and
ganoids alone existed ; and in this case, according to the standard
of highness chosen, so will it be said that fishes have advanced cr
retrograded in organisation. To attempt to compare members ci
distinct types in the scale of highness seems hopeless ; who will
decide whether a cuttle-fish be higher than a bee — that insect which
the great Von Baer believed to be " in fact more highly organised
than a fish, although upon another type " ? In the complex struggle
for life it is quite credible that crustaceans, not very high in their

Chap. XI.J ANCIENT AND LIVING FORK'S. 309

own class, might beat ceplialopods, the highest molluscs ; and such
crustaceans, though not highly developed, would stand very high in
the scale of invertebrate animals, if judged by the most decisive of
all trials — the law of battle. Besides these inherent difficulties in de-
ciding which forms are the most advanced in organisation, we ought
not solely to compare the highest members of a class at any two
periods — though undoubtedly this is one and perhaps the most
important element in striking a balance — but we ought to compare
all the members, high and low, at the two periodis. At an ancient
epoch the highest and lowest molluscoidal animals, namely, cephalo-
pods and brachiopods, swarmed in numbers ; at the present time both
groups are greatly reduced, whilst others, intermediate in organisatioUj
have largely increased; consequently some naturalists maintain
that molluscs were formerly more highly developed than at present ;
but a stronger case can be made out on the opposite side, by con-
sidering the vast reduction of brachiopods, and the fact that our
existing cephalopods, though few in number, are more highly orga-
nised than their ancient representatives. We ought also to compare
the relative proportional numbers at any two periods of the high and
low classes throughout the world : if, for instance, at the present
day fifty thousand kinds of vertebrate animals exist, and if we knew
that at some former period only ten thousand kinds existed, we
ought to look at this increase in number in the highest class, which
implies a great displacement of lower forms, as a decided advancb
in the organisation of the world. We thus see how hopelessly
difficult it is to compare with perfect fairness, under such extremely
complex relations, the standard of organisation of the imperfectly-
known faunas of successive periods.

We shall appreciate this difficulty more clearly, by looking to
certain existing faunas and floras. From the extraordinary manner
in which European productions have recently spread over New
Zealand, and have seized on places which must have been prc^viously
occupied by the indigenes, we must believe, that if all the animals
and plants of Great Britain were set free in New Zealand, a multi-
tude of British forms would in the course of time become thoroughly
naturalised there, and would exterminate many of the natives. On
the other hand, from the fact that har ily a single inhabitant of the
southern hemisphere has become wil I in any part of Europe, we
may well doubt whether, if all the productions of New Zealand were
set free in Great Britain, any considerable number would be enabled
to seize on places now occupied by OLr native plants and animals.
Under this point of view, the productions of Great Britain stand
much higher in the scale than those of New Zealand. Yet the

310 SUCCESSION OF THE [Chap. XI.

most skillul naturalist, I'rom an examination of the species of the
two countries, could not have foreseen this result.

Agassiz and several other highly competent judges insist that
ancient animals resemble to a certain extent the embryos of recent
animals belonging to the same classes ; and that the geological suc-
cession of extinct forms is nearly parallel with the embryological
development of existing forms. This view accords admirably well
with our theory. In a future chapter I shall attempt to show that
the adult differs from its embryo, owing to variations having
supervened at a not early age, and having been inherited at a
corresponding age. This process, whilst it leaves the embryo
almost unaltered, continually adds, in the course of successive
generations, more and more difterence to the adult. Thus the
embryo comes to be left as a sort of picture, preserved by nature, of
the former and less modified condition of the species. This view
may be true, and yet may never be capable of proof. Seeing, for
instance, that the oldest known mammals, reptiles, and fishes
strictly belong to their proper classes, though some of these old
forms are in a slight degree less distinct from each other than are
the typical members of the same groups at the present day, it
would be vain to look for animals having the common embryological
character of the Yertebrata, until beds rich in fossils are discovered
far beneath the lowest Cambrian strata — a discovery of which the
chance is small.

On the Succession of the same Types within the same Areas,
during the later Tertiary periods.

Mr. Clift many years ago showed that the fossil mammals from
the Australian caves were closely allied to the living marsupials
of that continent. In South America, a similar relationship is
manifest, even to an uneducated eye, in the gigantic pieces of
armour, like those of the armadillo, found in several parts of La
Plata ; and Professor Owen has shown in the most striking manner
that most of the fossil mammals, buried there in such numbers, are
related to South American types. This relationship is even more
clearly seen in the wonderful collection of fossil bones made by MM.
Lund and Clausen in the caves of Brazil. I was so much impressed
with these facts that I strongly insisted, in 1839 and 1845, on this
*' law of the succession of types," — on " this wonderful relationship
in the same continent between the dead and the living.'* Professor
Owen has subsequently extended the same generalisation to the
mammals of the Old World. We see the same law in this authors
restorations of the extinct and gigantic birds of New Zealand. We

CiiAP. XI.] SAME TYPES IN THE SAME AREAS. 311

see it also in the birds of the caves of Brazil. Mr. Woodward has
shown that the same law holds good with sea-shells, but, from the
wide distribution of most molluscs, it is not well displayed by
them. Other cases could be added, as the relation between the
extinct and living land-shells of Madeira ; and between the extinct
and living brackish water-shells of the Aralo-Caspian Sea.

Now what does this remarkable law of the succession of the
same types within the same areas mean ? He would be a bold man
who, after comparing the present climate of Australia and of parts of
South America, under the same latitude, would attempt to account,
on the one hand through dissimilar physical conditions, for the
dissimilarity of the inhabitants of these two continents ; and, on the
-other hand through similarity of conditions, for the uniformity of
the same types in each continent during the later tertiary periods.
Nor can it be pretended that it is an immutable law that marsupials
should have been chiefly or solely produced in Australia ; or that
Edentata and other American types should have been solely produced
in South America. For we know that Europe in ancient times was
XDCopled by numerous marsupials ; and I have shown in the publi-
cations above alluded to, that in America the law of distribution of
terrestrial mammals was formerly different from what it now is.
North America formerly partook strongly of the present character
of the southern half of the continent; and the southern half was
formerly more closely allied, than it is at present, to the northern
half. In a similar manner we know, from Falconer and Cautley's
^discoveries, that Northern India was formerly more closely related in
its mammals to Africa than it is at the present time. Analogous facts
'Could be given in relation to the distribution of marine animals.

On the theory of descent with modification, the great law of the
long enduring, but not immutable, succession of the same types
within the same areas, is at once explained ; for the inhabitants
'Of each quarter of the world will obviously tend to leave in that
•quarter, during the next succeeding period of time, closely allied
though in some degree modified descendants. If the inhabitants
^of one continent formerly differed greatly from those of another
continent, so will their modified descendants still differ in nearly
the same manner and degree. But after very long intervals of
time, and after great geographical changes, permitting much inter-
migration, the feebler will yield to the more dominant forms, and
there will be nothing immutable in the distribution of organic
beings.

It may be asked in ridicule, whether I suppose that the megathe-
trium and other aUied huge monsters, which formerly lived in

312 SUMMARY OF THE [Chap. XL

South America, have left behind them the sloth, armadillo, and
anteater, as their degenerate descendants. This cannot for an
instant be admitted. These huge animals have become wholly
extinct, and have left no progeny. But in the cavc-s of Brazil,
there are many extinct species which are closely allied in size and
in all other characters to the species still living in South America ;,
and some of these fossils may have been the actual progenitors of
the living species. It must not be forgotten that, on our theory,
all the species of the same genus are the descendants of some one
species ; so that, if six genera, each having eight species, be found in
one geological formation, and in a succeeding formation there be six
other allied or representative genera each with the same number of
species, then we may conclude that generally only one species of each
of the older genera has left modified descendants, whi-ch constitute
the new genera containing the several species; the other seven
species of each old genus having died out and left no progeny. Or,
and this will be a far commoner case, two or three species in two
or three alone of the six older genera will be the parents of the new
genera : the other species and the other whole genera havin«g become
utterly extinct. In failing orders, with the genera and species
decreasing in numbers as is the case with the Edentata of South
America, still fewer genera and species will leave modified blood-
descendants.

Summary of the preceding and present Chapters.

I have attempted to show that the geological record is extremely
imperfect ; that only a small portion of the globe has been geo-
logically explored with care ; that only certain classes of organic
beings have been largely preserved in a fossil state ; that the
number both of specimens and of species, preserved in our museums,
is absolutely as nothing compared with the number of generations
which must have passed away even during a single formation ; that,
owing to subsidence being almost necessary for the accumulation
of deposits rich in fossil species of many kinds, and thick enough to
outlast future degradation, great intervals of time must have elapsed
between most of our successive formations ; that there has probably
been more extinction during the periods of subsidence, and more
variation during the periods of elevation, and during the latter tho
record will have been least perfectly kept; that each single forma-
tion has not been continuously deposited ; that the duration of
each formation is, probably short compared with the average dura-
tion of specific forms ; that migration has played an important part
in the first appearance of new forms in any one area and formation •

Cv.^T. XI. j PRECEDING AND PRESENT CHAPTERS. 313

that widely ranging species are those which have varied mcst fre-
quently, and have oftenest given rise to new species ; that varieties
have at first been local; and lastly, although each species must
have passed through numerous transitional stages, it is probable
that the periods, during which each underwent modification, though
many and long as measured by years, have been short in com-
parison with the periods during which each remained in an un-
changed condition. These causes, taken conjointly, will to a large
extent explain why — though we do find many links — we do not
find interminable varieties, connecting together all extinct and
existing forms by the finest graduated steps. It should also be
constantly borne in mind that any linking variety between two
forms, which might be found, would be ranked, unless the whole
chain could be perfectly restored, as a new and distinct species ;
for it is not pretended that we have any sure criterion by which
species and varieties can be discriminated.

He who rejects this view of the imperfection of the geological
record, will rightly reject the whole theory. For he may ask in
vain where are the numberless transitional links which must
formerly have connected the closely allied or representative species,
found in the successive stages of the same great formation ? He
may disbelieve in the immense intervals of time which must have
elapsed between our consecutive formations ; he may overlook how
important a part migration has played, when the formations of any
one great region, as those of Europe, are considered ; he may urge
the apparent, but often falsely apparent, sudden coming in of whole
groups of species. He may ask where are the remains of those
infinitely numerous organisms which must have existed long before
the Cambrian system was deposited ? We now know that at least
one animal did then exist; but I can answer this last question
only by supposing that where our oceans now extend they have
extended for an enormous period, and where our oscillating con-
tinents now stand they have stood since the commencement of the
Cambrian system ; but that, long before that epoch, the world pre-
sented a widely different aspect ; and that the older continents,
formed of formations older than any known to us, exist now only
as remnants in a metamorphosed condition, or lie still buried under
the ocean.

Passing from these difficulties, the other great leading facts in
palajontology agree admirably with the theory of descent with
modification through variation and natural selection. We can thus
understand how it is that new species come in slowly and succes-
sively ; how species of different classes do not necessarily change

ol4 SU]\niAKY OF THK [Chap. XL

together, or at the same rate, or in the same degree ; yet in the
long run that all undergo modification to some extent. The ex-
tinction of old forms is the almost inevitable consequence of the
production of new forms. We can understand why when a species
has once disappeared it never reappears. Groups of species increase
in numbers slowly, and endure for unequal periods of time ; for tiie
process of modification is necessarily slow, and depends on many
complex contingencies. The dominant species belonging to large
and dominant groups tend to leave many modified descendants,
which form new sub-groups and groups. As these are formed, the
species of the less vigorous groups, from their inferiority inherited
from a common progenitor, tend to become extinct together, and
to leave no modified offspring on the face of the earth. But the
utter extinction of a whole group of species has sometimes been
a slow process, from the survival of a few descendants, lingering
in protected and isolated situations. When a group has once wholly
disappeared, it do^s not reappear ; for the link of generation has
been broken.

We can understand how it is that dominant forms which spread
widely and yield the greatest number of varieties tend to people the
world with allied, but modified, descendants ; and these will gene-
rally succeed ^n displacing the groups which are their inferiors in
the struggle for existence. Hence, after long intervals of time, the
productions of the world appear to have changed simultaneously.

We can understand how it is that all the forms of life, ancient
and recent, make together a few grand classes. We can under-
stand, from the continued tendency to divergence of character,. why
the more ancient a form is, the more it generally differs from those
now living ; why ancient and extinct forms often tend to fill up
gaps between existing forms, sometimes blending two groups, jore-
viously classed as distinct, into one ; but more commonly bringing
them only a little closer together. The more ancient a form is, the
more often it stands in some degree intermediate between groups
now distinct ; for the more .ancient a form is, the more nearly it
will be related to, and consequently resemble, the common pro-
genitor of groups, since become widely divergent. Extinct forms
are seldom directly intermediate between existing forms ; but are
intermediate only by a long and circuitous course through other
extinct and different forms. We can clearly see why the organic
remains of closely consecutive formations are closely allied ; for
they are closely linked together by generation. We can clearly see
why the remains of an intermediate formation are intermediate in
character.

Crap. XL] PRECEDING AND PRESENT CHAPTERS. 315

The inhabitants of the world at each successive period in its
history have beaten their predecessors in the race for life, and
are, in so far, higher in the scale, and their structure has gene-
rally become more specialised ; and this may account for the com-
mon belief held by so many palaeontologists, that organisation on
the whole has progressed. Extinct and ancient animals resemble
to a certain extent the embryos of the more recent animals belong-
ing to the same classes, and this wonderful fact receives a simple
■explanation according to our views. The succession of the same
types of structure within the same areas during the later geological
periods ceases to be mysterious, and is intelligible on the principle
of inheritance.

If then the geological record be as imperfect as many believe, and
it may at least be asserted that the record cannot be proved to be
much more perfect, the main objections to the theory of natural
selection are greatly diminished or disappear. On the other hand,
all the chief laws of palseontology plainly proclaim, as it seems to
ine, that species have been produced by ordinary generation : old
forms having been supplanted by new and improved forms of life,
the products of Yariation and the Survival of the Tittost.

316 GEOGRiPHlCAL DISTRIBUTIOX. fCiiAP. aIL

I

CHAPTER XIL

Geographical Distribution.

Present distribution cannot be accounted for by ditierences in physica.
conditions — Importance of barriers — Affinity of the productions of the
same continent — Centres of creation — Means of dispersal by changes
of climate and of the level of the land, and by occasional means —
Dispersal during the Glacial period — Alternate Glacial periods in the
North and South.

In considering the distribution of organic beings over the face of
the globe, the first great fact which strikes lis is, that neither the
similarity nor the dissimilarity of the inhabitants of various regions
can be wholly accounted for by climatal and other physical con-
ditions. Of late, almost every author who has studied the subject
has come to this conclusion. The case of America alone would
almost suffice to prove its truth : for if we exclude the arctic
and northern temperate parts, all authors agree that one of the
most fundamental divisions in geographical distribution is that
between the New and Old Worlds; yet if we travel over the
vast American continent, from the central parts of the United
States to its extreme southern point, we meet with the most
diversified conditions; humid districts, arid deserts, lofty moun-
tains, grassy plains, forests, marshes, lakes, and great rivers, under
almost every temperature. There is hardly a climat© or condition
in the Old World which cannot be paralleled in the New — at
least as closely as the same species generally require. No doubt
small areas can be pointed out in the Old World hotter than any in
the New World, but these are not inhabited by a fauna different
from that of the surrounding districts ; for it is rare to find a group
of organisms confined to a small area, of which the conditions are
peculiar in only a slight degree. Notwithstanding this general
parallelism in the conditions of the Old and New Worlds, how
widely different are their living productions !

In the southern hemisphere, if we compare large tracts of land m
Australia, South Africa, and western South America, between lati-
tudes 25° and 35°, we shall find parts extremely similar in all their

€iup. XII.] GEOGRAPHICAL DISTRIBUTION. 317

conditions, yet it would not be possible to point out three faunas
and floras more utterly dissimilar. Or, again, we may compare the
productions of South America south of lat. 35° with those north of
25°, which consequently are separated by a space of ten degrees
of latitude and are exposed to considerably different conditions, yet
they are incomparably more closely related to each other than they
are to the productions of Australia or Africa under nearly the same
climate. Analogous facts could be given with respect to the inha-
bitants of the sea.

A second great fact which strikes us in our general review is,
that barriers of any kind, or obstacles to free migration, are related
in a close and important manner to the differences between the
productions of various regions. We see this in the great difference
in nearly all the terrestrial productions of the New and Old Worlds,
excepting in the northern parts, where the land almost joins, and
where, under a slightly different climate, there might have been
free migration for the northern temperate forms, as there now is for
the strictly arctic productions. We see the same fact in the great
difference between the inhabitants of Australia, Africa, and South
America under the same latitude ; for these countries are ahnost as
much isolated from each other as is possible. On each continent,
also, we see the same fact ; for on the opposite sides of lofty and
continuous mountain-ranges, of great deserts, and even of large
rivers, we find different productions ; though as mountain-chains,
deserts, &c., are not as impassable, or likely to have endured so
long, as the oceans separating continents, the differences are very
inferior in degree to those characteristic of distinct continents.

Turning to the sea, we find the same law. The marine inha-
bitants of the eastern and western shores of South America are
very distinct, with extremely few shells, Crustacea or echinoder-
mata in common ; but Dr. Glinthcr has recently shown that about
thirty per cent, of the fishes are the same on the opposite sides
of the isthmus of Panama; and this fact has led naturalists to
believe that the isthmus was formerly open. Westward of the
shores of America, a wide space of open ocean extends, with not
an island as a halting-place for emigrants ; here we have a barrier
of another kind, and as soon as this is passed we meet in the eastern
islands of the Pacific with another and totally distinct fauna. So
that three marine faunas range far northward and southward in
parallel lines not far from each other, under corresponding climates ;
but from being separated from each other by impassable barriers
either of land or open sea, they are almost wholly distinct. On the
other hand, proceeding still farther westward from the eastern

318 GEOGRAPHICAL DISTRIBUTION. [Chap. XII.

islands of the tropical parts of the Pacific, we encounter no im-
passable barriers, and we have innumerable islands as halting-
]3laces, or continuous coasts, until, after travelling over a hemisphere,
we come to the shores of Africa ; and over this vast space we meet
with no well-defined and distinct marine faunas. Although so few
marine animals are common to the above-named three approximate
faunas of Eastern and Western America and the eastern Pacific
islands, yet many fishes range from the Pacific into the Indian
Ocean, and many shells are common to the eastern islands of the
Pacific and the eastern shores of Africa on almost exactly opposite
meridians of longitude.

A third great fact, partly included in the foregoing statement, is
the affinity of the productions of the same continent or of the same
sea, though the species themselves are distinct at different points
and stations. It is a law of the widest generality, and every con-
tinent offers innumerable instances. Nevertheless the naturalist, in
travelling, for instance, from north to south, never fails to be struck
by the manner in which successive groups of beings, specifically
distinct, though nearly related, replace each other. He hears from
closely allied, yet distinct kinds of birds, notes nearly similar, and
sees their nests similarly constructed, but not quite alike, with eggs
coloured in nearly the same manner. The plains near the Straits of
Magellan are inhabited by one species of Khea (American ostrich),
and northward the plains of La Plata by another species of the same
genus ; and not by a true ostrich or emu, like those inhabiting
Africa and Australia under the same latitude. On these same plains
of La Plata, we see the agouti and bizcacha, animals having nearly
the same habits as our hares and rabbits and belonging to the same
order of Rodents, but they plainly display an American type of
structure. We ascend the lofty peaks of the Cordillera, and we find
an alpine species of bizcacha ; we look to the waters, and we do not
find the beaver or musk-rat, but the coypu and capybara, rodents
of the S. American type. Innumerable other instances could be
given. If we look to the islands off the American shore, however
much they may differ in geological structure, the inhabitants are
essentially American, though they may be all peculiar species. We
may look back to past ages, as shown in the last chapter, and we
find American types then prevailing on the American continent and
in the American seas. We see in these facts some deep organic
bond, throughout space and time, over the same areas of land and
water, independently of physical conditions. The naturalist must
be dull, who is not led to inquire what this bond is.

The bond is simply inheritance, that cause which alone, as far as

OiUP. XII.] GEOGRAPHICAL DISTRIBUTION. ol^

we positively know, produces organisms quite like each other, or,,
as we see in the case of varieties, nearly alike. The dissimilarity of
the inhabitants of different regions may be attributed to modification
through variation and natural selection, and probably in a suV
ordinate degree to the definite infiuence of different physical con-
ditions. The degrees of dissimilarity will depend on the migration
of the more dominant forms of life from one region into another
having been more or less effectually prevented, at periods more or
less remote ; — on the nature and number of the former immigrants ;
— and on the action of the inhabitants on each other in leading to
the preservation of different modifications ; the vplation of organism
to organism in the struggle for life being, as I have already often
remarked, the most important of all relations. Thus the high im-
portance of barriers comes into play by checking migration ; as does
time for the slow process of modification through natural selection.-
Widely-ranging species, abounding in individuals, which have already
triumphed over many competitors in their own widely-extended
homes, will have the best chance of seizing on new places, when they
spread into new countries. In their new homes they will be ex-
posed to new conditions, and will frequently undergo further modi-
fication and improvement ; and thus they will become still further
victorious, and will produce groups of modified descendants. On this
principle of inheritance with modification, we can understand how it
is that sections of genera, whole genera, and even families, are con-
fined to the same areas, as is so commonly and notoriously the case.

There is no evidence, as was remarked in the last chapter, of the
existence of any- law of necessary development. As the variability
of each species is an independent property, and will be taken advan-
tage of by natm-aL selection, only so far as it profits each individual
in its complex struggle for life, so the amount of modification in
different species will be no uniform quantity. If a number of species,
after having long competed with each other in their old home, were
to migrate in a body into a new and afterwards isolated country,
they would be little liable to modification ; for neither migration
nor isolation in themselves efi'ect anything. These principles come
into play only by bringing organisms into new relations with each
other, and in a lesser degree with the surrounding physical conditions.
As we have seen in the last chapter that some forms have retained
nearly the same character from an enormously remote geological
period, so certain species have migrated over vast spaces, and have
not become greatly or at all modified.

According to these views, it is obvious that the several species of
the same genuS; though inhabiting the most distant quarters of the

322 SINGLE CENTRES OF CREATION. [Chap. XII.

from a siugle birthplace ; then, considering our ignorance with re-
Bpect to former climatal and geographical changes and to the various
fxxjasional m?ans of transport, the hehef that a single birthplace is
the law, seems to me incomparably the safest.

In discussing this subject, we shall be enabled at the same time
to consider a point equally important for us, namely, whether the
several species of a genus, which must on our theory all be descended
from a common progenitor, can have migrated, undergoing modi-
fication during their migration, from some one area. If, when most
of the species inhabiting one region are different from those of
p.cother region, though closely allied to them, it can be shown that
migration from the one region to the other has probably occurred
at some former period, our general view will be much strengthened ;
for the explanation is obvious on the principle of descent with modi-
fication. A volcanic island, for instance, upheaved and formed at
the distance of a few hundreds of miles from a continent, would
probably receive from it in the course of time a few colonists,
and their descendants, though modified, would still be related by
inheritance to the inhabitants of -that continent. Cases of this
nature are common, and are, as we shall hereafter see, inexplicable
on the theory of independent creation. This view of the relation of
the species of one region to those of another, does not differ much
from that advanced by Mr. Wallace, who concludes that " every
species has come into existence coincident both in space and time
with a pre-existing closely allied species." And it is now well
known that he attributes this coincidence to descent with modi-
iication.

The question of single or multiple centres of creation differs
from another though allied question, — namely, whether all the
individuals of the same species are descended from a single pair, or
single hermaphrodite, or whether, as some authors suppose, from
many individuals simultaneously created. With organic beings
which never intercross, if such exist, each species must be de-
scended from a succession of modified varieties, that have sup-
planted each other, but have never blended with other individuals
or varieties of the same species ; so that, at each successive stage
of modification, all the individuals of the same form will be de-
scended from a single parent. But in the great majority of cases,
namely, with all organisms which habitually unite for each birth,
or which occasionally intercross, the individuals of the same species
inhabiting the same area will be kept nearly uniform by inter-
crossing ; so that many individuals will go on simultaneously
changing, and the whole amount of modification at each stage will

CtiAP. XII.] MEANS OF DISPERSAL. 323

not be due to descent from a single parent. To illustrate what
I mean : our English race-horses differ from the horses of every
other breed ; but they do not owe their difference and superiority
to descent from aay single pair, but to continued care in the
selecting and training of many individuals during each generation.

Before discussing the three classes of facts, which I have selected
as presenting the greatest amount of difficulty on the theory of
" single centres of creation," I mast say a few words on the meaus
of dispersal.

Means of Dispersal.

Sir C. Lyell and other authors have ably treated this subject.
I can give here only the briefest abstract of the more important facts.
Change of climate must have had a powerful influence on migration.
A region now impassable to certain organisms from the nature of
its climate, might have been a high road for migration, when the
climate was different. I shall, however, presently have to discuss
this branch of the subject in some detail. Changes of level in the
land must also have been highly influential : a narrow isthmus
now separates two marine faunas ; submerge it, or let it formerly
have been submerged, and the two faunas will now blend together,
or may formerly have blended. Where the sea now extends, land
may at a former period have connected islands or possibly even
continents together, and thus have allowed terrestrial productions
to pass from one to the other. No geologist disputes that great
mutations of level have occurred within the period of existing
organisms. Edward Forbes insisted that all the islands in the
Atlantic must have been recently connected with Europe or Africa,
.and Europe likewise with America. Other authors have thus
hypothetically bridged over every ocean, and united almost every
island to some mainland. If indeed the arguments used by Forbes
are to be trusted, it must be admitted that scarcely a single island
exists which has not recently been united to some continent. This
view cuts the Gordian knot of the dispersal of the same species to
the most distant points, and removes many a difficulty ; but to the
best of my judgment we are not authorized in admitting such
enormous geographical changes within the period of existing species.
It seems to me that we have abundant evidence of great oscillations
in the level of the land or sea ; but not of such vast changes in the
position and extension of our continents, as to have united them
within the recent period to each other and to the several intervening
oceanic islands. I freely admit the former existence of many islands,
now buried beneath the sea^ which msyhave served as halting-

Y 2

Stale Hisionca! ai.o
Ki^.tur'..! Hi^Torv Society,

324 MEANS OF DISPERSAL. [Chap. XII.

places for plants and for many animals during their migration. In
the coral-producing oceans such sunken islands are now marked by
rings of coral or atolls standing over them . Whenever it is fully
admitted, as it will some day be, that each species has proceeded
from a single birthplace, and when in the course of time we know
something definite about the means of distribution, we shall be
enabled to speculate with security on the former extension of the
land. But I do not believe that it will ever be proved that within
the recent period most of our continents which now stand quite
separate, have been continuously, or almost continuously united
with each other, and with the many existing oceanic islands.
Several facts in distribution, — such as the great difference in the
marine faunas on the opposite sides of almost every continent, —
the close relation of the tertiary inhabitants of several lands and
even seas to their present inhabitants, — the degree of affinity be-
tween the mammals inhabiting islands with those of the nearest
continent, being in part determined (as we shall hereafter see) by
the depth of the intervening ocean, — these and other such facts are
opposed to the admission of such prodigious geographical revolutions
within the recent period, as are necessary on the view advanced by
Forbes and admitted by his followers. The nature and relative pro-
portions of the inhabitants of oceanic islands are likewise opposed
to the belief of their former continuity with continents. Nor does
the almost universally volcanic composition of such islands favour
the admission that they are the wrecks of sunken continents ; — it
they had originally existed as continental mountain-ranges, some at
least of the islands would have been formed, like other mountain-
summits, of granite, metamorphic schists, old fossiliferoas and other
rocks, instead of consisting of mere piles of volcanic matter.

I must now say a few words on what are called accidental means,
but which more properly should be called occasional means of dis-
tribution. I shall here confine myself to plants. In botani<;al
works, this or that plant is often stated to be ill adapted for wide
dissemination ; but the greater or less facilities for transport across
the sea may be said to be almost wholly unknown. Until I tried,
with Mr. Berkeley's aid, a few experiments, it was not even known
how far seeds could resist the injurious action of sea- water. To
my surprise I found that out of 87 kinds, 64 germinated after an
immersion of 28 days, and a few survived an immersion of 137
days. It deserves notice that certain orders were far more injured
than others : nine Leguminosje were tried, and, with one exception,
they resisted the salt-water badly ; seven species of the allied orders,
Hydrophyllaceai and PciemciniaceEe, were all killed by a month's

Chap. XII.] MEANS OF DISPERSAL. 325

immersion. I^or convenience' sake I chiefly tried small seeds,
without the capsule or fruit ; and as all of these sank in a few days,
they could not have been floated across wide spaces of the sea,
whether or not they were injured by the salt-water. Afterwards
I tried some larger fruits, capsules, &c., and some of these floated
for a long time. It is well known what a diifeiKence there is in the
buoyancy of green and seasoned timber ; and it occurred to me that
Hoods would often wash into the sea dried plants or branches with
seed-capsules or fruit attached to them. Hence I was led to dry the
stems and branches of 94 plants with ripe fruit, and to place them
on sea-water. The majority sank quickly, but some which, whilst
green, floated for a very short time, when dried floated much longer ;
for instance, ripe hazel-nuts sank immediately, but when dried
they floated for 90 days, and afterwards when planted germinated ;
an asparagus-plant with ripe berries floated for 23 days, when dried
it floated for 85 days, and the seeds afterwards germinated ; the
ripe seeds of Helosciadium sank in two days, when dried they
floated for above 90 days, and afterwards germinated. Altogether,
out of the 94 dried plants, 18 floated for above 28 days ; and
some of the 18 floated for a very much longer period. So that as
-^^ kinds of seeds germinated after an immersion of 28 days ; and
as if distinct species with ripe fruit (but not all the same species
as in the foregoing experiment) floated, after being dried, for above
28 days, we may conclude, as far as anything can be inferred from
these scanty facts, that the seeds of ^J-^q kmds of plants of any
country might be floated by sea-currents during 28 days, and would
retain their power of germination. In Johnston's Physical Atlas,
the average rate of the several Atlantic currents is 33 miles per
diem (some currents running at the rate of 60 miles per diem) ; on
this average, the seeds of -^^ plants belonging to one country
might be floated across 924 miles of sea to another country, and
when stranded, if blown by an inland gale to a favourable spot,
would germinate.

Subsequently to my experiments, M. Martens tried similar ones,
but in a much better manner, for he placed the seeds in a box in
the actual sea, so that they were alternately wet and exposed to the
air like really floating plants. He tried 98 seeds, mostly difi'erent
from mine ; but he chose many large fruits and likewise seeds from
plants which live near the sea ; and this would have favoured both
the average length of their flotation and their resistance to the
injurious action of the salt-water. On the other hand, he did not
previously dry the plants or branches with the fruit ; and this, as
ire have seen, would have caused some of them to have fi<.)ated

326 MEANS OF DISPEESAL. [Chap. XII,

much longer. The result was that ^ of his seeds of different
kinds floati^d for 42 days, and were then capable of germination.
But I do not doubt that plants exposed to the waves would fioiit
for a less time than those protected from violent movement as in
our experiments. Therefore it would perhaps be safer to assume
that tlie seeds of about JJ'q plants of a flora, after having been
dried, could be floated across a space of sea 900 miles in width, and
would then germinate. The fact of the larger fruits often floating
longer than the small, is interesting ; as plants with large seeds or
fruit which, as Alph. de CandoUe has shown, generally have re-
stricted ranges, could hardly be transported by any other means.

Seeds may be occasionally transported in another manner. Drift
timber is thrown up on most islands, even on those in the midst
of the widest oceans ; and the natives of the coral-islands in the
Pacific procure stones for their tools, solely from the roots of drifted
trees, these stones being a valuable royal tax. I find that when
irregularly shaped stones are embedded in tlie roots of trees, small
parcels of earth are frequently enclosed in their interstices and
behind them, — so perfectly that not a particle could be washed away
during the longest transport : out of one small portion of earth
thus completely enclosed by the roots of an oak about 50 years old,
three dicotyledonous plants germinated : I am certain of the accu-
racy of this observation. Again, I can show that the carcases of
birds, when floating on the sea, sometimes escape being immediately
devoured : and many kinds of seeds in the crops of floating birds
long retain their vitality : peas and vetches, for instance, are killed
by even a few days' immersion in sea-water ; but some taken out
of the crop of a pigeon, which had floated on artificial sea-water for
30 days, to my surprise nearly all germinated.

Living birds can hardly fail to be highly effective agents in the
transportation of seeds. I could give many facts showing how
frequently birds of many kinds are blown by gales to vast distances
across the ocean. We may safely assume that under such circum-
stances their rate of flight would often be 35 miles an hour ; and
some authors have given a far higher estimate. I have never seen
an instance of nutritious seeds passing through the intestines of
a bird ; but hard seeds of fruit pass uninjured through even the
digestive organs of a turkey. In the course of two months, I picked
up in my garden 12 kinds of seeds, out of the excrement of small
birds, and these seemed perfect, and some of them, which were
tried, germinated. But the following fact is more important : the
crops of birds do not secrete gastric juice, and do not, as I know by
trial, injure in the least the germination of seeds ; now, after a bird

Canp. XII,] MEANS OF DISPERSAL. 327

has found and dcovured a large sup])ly of food, it is positively
asserted that all the grains do not pass into the gizzard for twelve
or even eighteen hours. A bird in this interval might easily bo
blown to the distance of 500 miles, and hawks are known to look
out for tired birds, and the contents of their torn crops might thus
readily get scattered. Some hawks and owls bolt their prey whole,
and, after an interval of from twelve to twenty hours, disgorge
pellets, which, as I know from experiments made in the Zoological
Gardens, include seeds capable of germination. Some seeds of the
oat, wheat, millet, canary, hemp, clover, and beet germinated aftei
having been from twelve to twenty-one hours in the stomachs of
different birds of prey; and two seeds of beet grew after having
b^en thus retained for two days and fourteen hours. Fresh-water
fish, I find, eat seeds of many land and water plants: fish are
frequently devoured by birds, and thus the seeds might be trans-
ported from place to place. I forced many kinds of seeds into the
stomachs of dead fish, and then gave their bodies to fishing-eagles,
stoi'ks, and pelicans ; these birds, after an interval of many hours,
either rejected the seeds in pellets or passed them in their excre-
ment ; and several of these seeds retained the power of germination.
Certain seeds, however, were always killed by this process.

Locusts are sometimes blown to great distances from the land ; I
myself caught one 370 miles from the coast of Africa, and have
heard of others caught at greater distances. The Rev. R. T. Lowe
informed Sir C. Lyell that in November 1844 swarms of locusts
visited the island of Madeira. They were in countless numbers, as
thick as the flakes of snow in the heaviest snowstorm, and extended
upwards as far as could be seen with a telescope. During two or
three days they slowly careered rcand and roimd in an immense
elli|)se, at least five or six miles in diameter, and at night alighted
on the taller trees, which were completely coated with them. They
then disappeared over the ' sea, as suddenly as they had appeared,
and have not since visited the island. Now, in parts of Natal it is
believed by some farmers, though on insufiicient evidence, that
injurious seeds are introduced into their grass-land in the dung left
by the great flights of locusts which often visit that country. In
consequence of this belief Mr. Weale sent me in a letter a small
packet of the dried pellets, out of which I extracted under the
microscope several secda, and raised from them seven grass plants,
belonging to two species, of two genera. Hence a swarm of locusts,
such as that which visited Madeira, might readily be the means of
introducing several kinds of plants into an island lying far from Ihe
mainland.

328 MEANS OF DISPERSAL. [Chap. XIL

Although the beaks and feet of birds are generally clean, earth
sometimes adheres to them : in one case I removed sixty-one grains,
and in another case twenty-two grains of dry argillaceous earth
from the foot of a partridge, and in the earth there was a pebble as
large as the seed of a vetch. Here is a better case : the leg of a
woodcock was sent to me by a friend, with a little cake of dry earth
attached to the shank, weighing only nine grains ; and this con-
tained a seed of the toad-rush (Juncus bufonius) which germinated
and flowered. Mr. Swaysland, of Brighton, who during the last
forty years has paid close attention to our migratory birds, informs
me that he has often shot wagtails (Motacillas), wheatears, and whin-
chats (Saxicolas), on their first arrival on our shores, before they
had alighted ; and he has several times noticed little cakes of earth
attached to their feet. Many facts could be given showing how
generally soil is charged with seeds. For instance. Prof. Newton
sent me the leg of a red-legged partridge (Caccabis rufa) which had
been wounded and could not fly, with a ball of hard earth adhering
to it, and weighing six and a half ounces. The earth had been
kept for three years, but when broken, watered and placed under a
bell glass, no less than 82 plants sprung from it : these consisted of
12 monocotyledons, including the common oat, and at least one
kind of grass, and of 70 dicotyledons, which consisted, judging from
the young leaves, of at least three distinct species. With such facts
before us, can we doubt that the many birds which are annually
blown by gales across great spaces of ocean, and which annually
migrate — for instance, the millious of quails across the Mediterra-
nean— must occasionally transport a few seeds embedded in dirt
adhering to their feet or beaks ? But I shall have to recur to this
subject.

As icebergs are known to be sometimes loaded with earth and
stones, and have even carried brushwood, bones, and the nest of a
land-bird, it can hardly be doubted that they must occasionally, as
suggested by Lyell, have transported seeds from one part to another
of the arctic and antarctic regions; and during the Glacial period
from one part of the now temperate regions to another. In the
Azores, from the large number of plants common to Europe, in com-
parison with the species on the other islands of the Atlantic, which
stand nearer to the mainland, and (as remarked by Mr. H. C.
Watson) from their somewhat northern character in comparison
with the latitude, I suspected that these islands had been partly
stocked by ice-borne seeds, during the Glacial epoch. At my request
Sir C. Lyell wrote to M. Hartung to inquire whether he had
observed erratic boulders on these islands, and he answered that he

CuAP. XII.] MEANS OF DISPERSAL. 320

had found large fragments of granite and other rocks, which do not
occur in the archipelago. Hence we may safely infer that icebergs
formerly landed their rocky burthens on the shores of these mid-
ocean islands, auvl it is at least possible that they may have brought
thither some few seeds of northern plants.

Considering that these several means of transport, and that other
means, which without doubt remain to be discov^ered, have been in
action year after year for tens of thousands of years, it would, I
think, be a marvellous fact if many plants had not thus become
widely transported. These means of transport are sometimes called
accidental, but this is not strictly correct : the currents of the sea
are not accidental, nor is the direction of prevalent gales of wind,
it should be observed that scarcely any means of transport would
carry seeds for very great distances : for seeds do not retain their
vitality when exposed for a great length of time to the action of
sea-water; nor could they be long cari'icd in the crops or intestines
of birds. These means, however, would suffice for occasional trans-
port across tracts of sea some hundred miles in breadth, or from
island to island, or from a continent to a neighbouring island, but
not from one distant continent to another. The floras of distant
continents would not by such means become mingled ; but would
remain as distinct as they now are. The currents, from their
course, would never bring seeds from North America to Britain,
though they might and do bring seeds from the West Indies to our
western shores, where, if not killed by their very long immersion in
salt water, they could not endure our climate. Almost every year,
one or two land-birds are blown across the whole Atlantic Ocean,
from North America to the western shores of Ireland and England ;
but seeds could be transported by these rare wanderers only by
one means, namely, by dirt adhering to their feet or beaks, w^hich is
in itself a rare accident. Even in this case, how small would be the
chance of a seed falling on favourable soil, and coming to maturity I
But it would be a great error to argue that because a well-stocked
island, like Great Britain, has not, as far as is known (and it w^ould
be very difficult to prove this), received within the last few centu-
ries, through occasional means of transport, immigrants from Europe
or any other continent, that a poorly-stocked island, though stand-
ing more remote from the mainland, would not receive colonists by
similar means. Out of a hundred kinds of seeds or animals trans-
ported to an island, even if far less well- stocked than Britain, per-
haps not more than one would be so well fitted to its new home, as
to become naturalised. But this is no valid argument against what
wou^d be elTected by occasional means of transj^ort, during tlie Iod^

330 DISPERSAL DURING THE GLACIAL PERIOD. [CuAV. XII.

lapse of geological time, whilst the island was being upheaved, and
before it had become fully stocked with inhabitants. On almost
bare land, with few or no destructive insects or cirds living there,
nearly every seed which chanced to aiTive, if fitted, for the climate,
would germinate and survive.

Dispersal during the Glacial Perijd.

The identity of many plants and animals, on mountain-summits,
separated from each other by hundreds of miles of lowlands, where
Alpine species could not possibly exist, is one of the most striking
cases known of the same species living at distant points, without
the apparent jwssibility of their having migrated from one point
to the other. It is indeed a remarkable fact to see so many plants
of the same species living on the snowy regions of the Alps or
P^n-enecs, and in the extreme northern parts of Europe ; but it is
far more remarkable, that the plants on the White Mountains, in*
the United States of America, are all the same with those of
Labrador, and nearly all the same, as we hear from Asa Gray, with
those on the loftiest mountains of Europe. Even as long ago as
1747, such facts led Gmelin to conclude that the same species must
have been independently created at many distinct points ; and we
might have remained in this same belief, had not Agassiz and
others called vivid attention to the Glacial period, which, as we
shall immediately see, affords a simple explanation of these facts.
We have evidence of almost every conceivable kind, organic and
inorganic, that, within a very recent geological period, central
Europe and North America suffered under an arctic climate. The
ruins of a house burnt by fire do not tell their tale more plainly
than do the mountains of Scotland and Wales, with their scored
flanks, polished surfaces, and perched boulders, of the icy streams
with which their valleys were lately filled. So greatly has the
climate of Europe changed, that in Northern Italy, gigantic moraines,
left by old glaciers, are now clothed by the vine and maize. Through-
out a large part of the United States, erratic boulders and scored
rocks plainly reveal a former cold period.

The former influence of the glacial climate on the distribution of
the inhabitants of Europe, as explained by Edward Forbes, is sub-
stantially as follows. But we shall follow the changes more readily,
by supposing a new glacial period slowly to come on, and then
pass away, as formerly occurred. As the cold came on, and as
each more southern zone became fitted for the inhabitants of the
north, these would take the plac<cs cf the former inhabitants of
the temperate regions. The latter, at the same time, would travel

Chap. XII.] DISPERSAL DURING THE GLACIAL PERIOD. 331

fui^her and further southward, unless they were stopped by barriers,
in which case they would perish. The mountains would become
covered with snow and ice, and their former Alpine inhabitants
would descend to the plains. By the time that the cold had reached
its maximum, we should have an arctic fauna and flora, covering
th3 central parts of Europe, as far south as the Alps and Pyrenees,
and even stretching into Spain. The now temperate regions of the
United States would likewise be covered by arctic plants and ani-
mals and these would be nearly the same with those of Europe ; for
the present circumpolar inhabitants, which we suppose to have every-
where travelled southward, are remarkably uniform round the world.

As the warmth returned, the arctic forms would retreat north-
ward, closely followed up in their retreat by the productions of the
more temperate regions. And as the snow melted from the bases
of the mountains, the arctic forms would seize on the cleared
and thawed ground, always ascending, as the warmth increased and
the snow still further disappeared, higher and higher, whilst their
brethren were pursuing their northern journey. Hence, when the
warmth had fully returned, the same species, which had lately
lived together on the European and North American lowlands,
would again be found in the arctic regions of the Old and New
Worlds, and on many isolated mountain-summits far distant from
each other.

Thus we can understand the identity of many plants at points
so immensely remote as the mountains of the United States and
those of Europe. We can thus also understand the fact that the
Alpine plants of each mountain- range are more especially related
to the arctic forms living due north or nearly due north of them :
for the first migration when the cold came on, and the re-migratior
on the returning warmth, would generally have been due south and
north. The Alpine plants, for example, of Scotland, as remarked
by Mr. H. C. Watson, and those of the Pyrenees, as remarked by
Eamond, are more especially allied to the plants of northern Scandi-
navia ; those of the United States to Labrador ; those of the moun-
tains of Siberia to the arctic regions of that country. These views,
grounded as they are on the perfectly well-ascertained occurrence of
a former Glacial period, seem to me to explain in so satisfactory a
manner the present distribution of the Alpine and Arctic produc-
tions of Europe and America, that when in other regions we find
the same species on distant mountain-summits, we may almost
conclude, without other evidence, that a colder climate formerly
permitted their migration across the intervening lowlands, now
become too warm for their existence.

332 DISPERSAL DURING TH^ GLACIAL PERIOD. Chap. XII.]

As the arctic forms moved first southward and aftervvra'ds back-
wards to the north, in unison with the changing climate, they will
not have been exposed during their long migrations to any great
diversity of temperature; and as they all migrated in a body
together, their mutual relations will not have been much disturbed.
Hence, in accordance wich the principles inculcated in this volume,
these forms will not have been liable to much modification. But
with the Alpine productions, left isolated from the moment of the
returning warmth, first at the bases and ultimately on the summits
of the mountains, the case will have been somewhat different ; for
it is not likely that all the same arctic species will have been left
on mountain-ranges far distant from each other, and have survived
there ever since ; they will also in all probability, have become
mingled with ancient Alpine species, which must liave existed on
the mountains before the commencement of the Glacial epoch, and
which during the coldest period will have been ten:)porarily driven
down to the plains ; they will, also, have been subsequently ex-
posed to somewhat different climatal influences. Their mutual rela-
tions will thus have been in some degree disturbed; consequently
they will have been liable to modification ; and they have been
modified ; for if we compare the present Alpine plants and animals
of the several great European mountain-ranges one with another,
though many of the species remain identically the same, some
exist as varieties, some as doubtful forms or sub-species, and
some as distinct yet closely allied species representing each other
on the several ranges.

In the foregoing illustration I have assumed that at the com-
mencement of our imaginary Glacial period, the arctic productions
were as uniform round the polar regions as they are at the present
day. But it is also necessary to assume that many sub-arctic and
some few temperate forms were the same round the world, for
some of the species which now exist on the lower mountain-slopes
and on the plains of North America and Europe are the same;
and it may be asked how I account for this degree of uniformity
in the sub-arctic and temperate forms round the world, at the
commencement of the real Glacial period. At the j^resent day,
the sub-arctic and northern temperate productions of the Old
and New Worlds are separated from each other by the whok
Atlantic Ocean and by the northern part of the Pacific. During
the Glacial period, when the inhabitants of the Old and Ne\/
Worlds lived farther southwards than they do at present, they
must have been still more completely separated from each othej
by wider spaces of ocean ; so that it may well be asl^ed now tno

CiiAi'. Xn.J DISPERSAL DURING THE GLACIAL PERICD. 333

same species could then or previously Lave entered the two con-
tinents. The explanation, I believe, lies in the nature of the
climate before the commencement of the Glacial period. At this,
the newer Pliocene period, the majority of the inhabitants of the
world were specifically the same as now, and we have good reason
to believe that the climate was warmer than at the present day
Hence we may suppose that the organisms which now live undei
latitude 60°, lived during the Pliocene period farther north under the
Polar Circle, in latitude 66°-67° ; and that the present arctic pro-
ductions then lived on the broken land still nearer to the pole.
Now, if we look at a terrestrial globe, we see under the Polar Circle
that there is almost continuous land from western Europe, through
Siberia, to eastern America. And this continuity of the circum-
polar land, with the consequent freedom under a more favourable
climate for intermigration, will account for the supposed uniformity
of the sub-arctic and temperate productions of the Old and New
Worlds, at a period anterior to the Glacial epoch.

Believing, from reasons before alluded to, that our continents
have long remained in nearly the same relative position, though
subjected to great oscillations of level, I am strongly inclined to
extend the above view, and to infer that during some still earlier
and still warmer period, such as the older Pliocene period, a large
number of the same plants and animals inhabited the almost
continuous circumpolar land ; and that these plants and animals,
both in the Old and New Worlds, began slowly to migrate south-
wards as the climate became less warm, long before the commence-
ment of the Glacial period. We now see, as I believe, their
descendants, mostly in a modified condition, in the central parts
of Europe and the United States. On this view we can under-
stand the relationship with very little identity, between the pro-
ductions of North America and Europe, — a relationship which is
highly remarkable, considering the distance of the two areas, and
their separation by the whole Atlantic Ocean. We can further
understand the singular fact remarked on by several observers
that the productions of Europe and America during the later
tertiary stages were more closely related to each other than they
are at the present time ; for during these warmer periods the
northern parts of the Old and New Worlds will have been almost
continuously united by land, serving as a bridge, since rendered
impassable by cold, for the intermigration of their inhabitants.

During the slowly decreasing warmth of the Pliocene period, as
Boon as the species in common, which inhabited the New and Old
Worlds, migrated south of the Polar Circle, they will have been

334: DISPERSAL DURING THE GLACIAL PERIOD. [Chap. XIL

completely cut oS from each other. This separation, as far as the
more temperate productions are concerned, must have taken place
long ages ago. As the plants and animals migrated southward,
they will have hecome mingled in the one great region with the
native American productions, and would have had to compete
with them ; and in the other great region, with those of the Old
World. Consequently we have here everything favourahle for
much modification, — for far more modification than with the
Alpine productions, left isolated, within a much more recent
period, on the several mountain-ranges and on the arctic lands
of Europe and N. America. Hence it has come, that when we
compare the now living productions of the temperate regions of
the New and Old Worlds, we find very few identical species (though
Asa Gray has lately shown that more plants are identical than was
formerly supposed), hut we find in every great class many forms,
which some naturalists rank as geographical races, and others as dis-
tinct species ; and a host of closely allied or representative forms
which are ranked hy all naturalists as specifically distinct.

As on the land, so in the waters of the sea, a slow southern
migration of a marine fauna, which, during the Pliocene or even a
somewhat earlier period, was nearly uniform along the continuous
shores of the Polar Circle, will account, on the theory of modifica-
tion, for many closely allied forms now living in marine areas com-
pletely sundered. Thus, I think, we can understand the presence
of some closely allied, still existing and extinct tertiary forms, on
the eastern and western shores of temperate North America ; and
the still more striking fact of many closely allied crustaceans (as
described in Dana's admirable work), some fish and other marine
animals, inhabiting the Mediterranean and the seas of Japan, —
these two areas being now completely separated by the breadth of a
whole continent and by wide spaces of ocean.

These cases of close relationship in species either now or formerly
inhabiting the seas on the eastern and western shores of North
America, the Mediterranean and Japan, and the temperate lands
of North America and Europe, are inexplicable on the theory of
creation. We cannot maintain that such species have been created
alike, in correspondence with the nearly similar physical conditions
of the areas ; for if we compare, for instance, certain parts of South
America with parts of South Africa or Australia, we see countries
closely similar in all their physical conditions, with their inhal>-
itants utterly dissimilar.

Chap. XII.] ALTERNATE GLACIAL PERIODS. 335

Alternate Qlacial Periods in the North and South.

■ But we must return to onr more immediate subject. 1 arc con-
vinced that Forbes's view may be largely extended. In Europe we
meet with the plainest evidence of the Glacial period, from the
western shores of Britain to the Oural range, and southward to the
Pyrenees. We may infer from the frozen mammals and nature
of the mountain vegetation, that Siberia was similarly affected. In
the Lebanon, according to Dr. Hooker, perpetual snow formerly
covered the central axis, and fed glaciers which rolled 4000 feet
down the valleys. The same observer has recently found great
moraines at a low level on the Atlas range in N. Africa. Along
the Himalaya, at points 900 miles apart, glaciers have left the
marks of their former low descent ; and in Sikkim, Dr. Hooker
saw maize growing on ancient and gigantic moraines. Southward
of the Asiatic continent, on the opposite side of the equator, we
know, from the excellent researches of Dr. J. Haast and Dr. Hector,
that in New Zealand immense glaciers formerly descended to a
low level ; and the same plants found by Dr. Hooker on widely
separated mountains in this island tell the same story of a former
cold period. From facts communicated to me by the Rev. W. B.
Clarke, it appears aho that there are traces of former glacial action
on the mountains of the south-eastern corner of Australia.

Looking to America ; in the northern half, ice-borne fragments of
rock have been observed on the eastern side of the continent, as far
south as lat. 36°-37°, and on the shores of the Pacific, v;here the
climate is now so different, as far south as lat. 46°. Erratic boulders
have, also, been noticed on the Rocky Mountains. In the Cor-
dillera of South America, nearly under the equator, glaciers once
extended far below their present level. In Central Chile I ex-
amined a vast mound of detritus with great boulders, crossing the
Portillo valley, which there can hardly be a doubt once formed a
huge moraine; and Mr. D. Forbes informs me that he found in
various parts of the Cordillera, from lat. 13° to 30° S., at about the
height of 12,000 feet, deeply-furrowed rocks, resembling those with
which he was familiar in Norway, and likewise great masses of
detritus, including grooved pebbles. Along this whole space of the
Cordillera true glaciers do not now exist even at much more con-
siderable heights. Farther south on both sides of the continent,
from lat. 41° to the southernmost extremity, we have the clearest
evidence of former glacial action, in numerous immense boulders
transported far from their parent source.

From these several facts, namely from the glacial action having

336 ALTERNATE GLACIAL PERIODS [Chap. XIl.

extended all round the nortiiern and southern hemispheres — from
the period having been in a geological sense recent in both hemi-
spheres—from its having lasted in both during a great length of
time, as may be inferred from the amount of work effected — and
lastly from glaciers having recently descended to a low level along;
the whole line of the Cordillera, it at one time appeared to me that
we could not avoid the conclusion that the temperature of the
whole world had been simultaneously lowered during the Glacial
period. But now Mr. CroU, in a series of admirable memoirs, has
attempted to show that a glacial condition of climate is the result
of various physical causes, brought into operation by an increase in
the eccentricity of the earth's orbit. All these causes tend towards
the saine end ; but the most powerful appears to be the indirect
influence of the eccentricity of the orbit upon oceanic currents.
According to Mr. Croll, cold periods regularly recur every ten or
fil'teen thousand years; and these at long intervals are extremely
severe, owing to certain contingencies, of which the most important,
as Sir C. Lyell has shown, is the relative position of the land and
water. Mr. Croll believes that the last great Glacial period occurred
about 240,000 years ago, and endured with slight alterations of
climate for about 1G0,000 years. With respect to more ancient
Glacial periods, several geologists are convinced from direct evidence
that such occurred during the Miocene and Eocene formations, not
to mention still more ancient formations. But the most important
result for us, arrived at by Mr. Croll, is that whenever the northern
hemisphere passes through a cold period, the temperature of the
southern hemisphere is actually raised, with the winters rendered
much milder, chiefly through changes in the direction of the ocean-
currents. So conversely it will be with the northern hemisphere,
whilst the southern passes though a glacial period. This conclusion
throws so much light on geographical distribution that I am
strongly inclined to trust in it ; but I will first give the facts, which
demand an explanation.

In South America, Dr. Hooker has shown that besides many
closelj'' allied species, between forty and fifty of the flowering plants
of Tierra del Fuego, forming no inconsiderable part of its scanty
flora, are common to North America and Europe, enormously
remote as these areas in opposite hemispheres are from each other.
On the lofty mountains of equatorial America a host of peculiar
Bpecies belonging to European genera occur. On the Organ moun-
tains of Brazil, some few temperate European, some Antarctic, and
some Andean genera were found by Gardner, which do not exist
In the low intervening hot countries. On the Silla of Caraccas»

Chap. XII.] IN THE NORTH AND SOUTH. 337

tlie illustrious Humboldt long ago found species belonging to j^enera
characteristic of the Cordillera.

In Africa, several forms characteristic of Europe and some few
representatives of the flora of the Cape of Good Hope occur on the
mountains of Abyssinia. At the Cape of Good Hope a very few
European species, believed not to have been introduced by man,
and on the mountains several representative European forms are
found, which have not been discovered in the intertropical parts of
Africa. Dr. Hooker has also lately shown that several of the plants
living on the upper parts of the lofty island of Fernando Po and on
the neighbouring Cameroon mountains, in the Gulf of Guinea, are
closely related to those on the mountains of Abyssinia, and likewise
to those of temperate Europe. It now also appears, as I hear from
Dr. Hooker, that some of these same temperate plants have been
discovered by the Rev. R. T. Lowe on the mountains of the Cape
Verde islands. This extension of the same temperate forms, almost
under the equator, across the whole continent of Africa and to
the mountains of the Caps Verde archipelago, is one of the most
astonishing facts ever recorded in the distribution of plants.

On the Himalaya, and on the isolated mountain-ranges of the
peninsula of India, on the heights of Ceylon, and on the volcanic
cones of Java, many plants occur, either identically the same or
representing each other, and at the same time representing plants
of Europe, not found in the intervening hot lowlands. A list of
the genera of plants collected on the loftier peaks of Java, raises
a picture of a collection made on a hillock in EurojDe ! Still more
striking is the fact that peculiar Australian forms are represented
by certain plants growing on the summits of the mountains of
Borneo. Some of these Australian forms, as I hear from Dr. Hooker,
extend along the heights of the peninsula of Malacca, and are
thinly scattered on the one hand over India, and on the other hand
as far north' as Japan.

On the southern mountains of Australia, Dr. F. Mtiller has
discovered several European species ; other species, not introduced
by man, occur on the lowlands ; and a long list can be given, as I
am informed by Dr. Hooker, of European genera, found in Australia,
but not in the intermediate torrid regions. In the admirable
* Introduction to the Flora of New Zealand,' by Dr. Hooker, analo-
gous and striking facts are given in regard to the plants of that
large island. Hence we see that certain plants growing on the more
lofty mountains of the tropics in all parts of the world, and on the
t'jmperate plains of the north and south, are either the same species
or varieties of the same species. It should, however, be observed

z

338 ALlERNATE GLACIAL PERIODS [Chap. XIi.

that these plants are not strictly arctic forms ; for, as Mr. H. C.
Watson has remarked, " in receding from polar towards equatorial
latitudes, the Alpine or mountain floras really become less and less
Arctic." Besides these identical and closely allied forms, many
species inhabiting the same widely sundered areas, belong to genera
not now found in the intermediate tropical lowlands.

These brief remarks apply to plants alone ; but some few analogous
facts could be given in regard to terrestrial animals. In marine
productions, similar cases likewise occur ; as an example, I may
(piote a statement by the highest authority. Prof. Dana, that " it is
certainly a wonderful fact that New Zealand should have a closer
resemblance in its Crustacea to Great Britain, its antipode, than to
any other part of the world." Sir J. Richardson, also, speaks ot
the reappearance on the shores of New Zealand, Tasmania, &c.,
of northern forms of fish. Dr. Hooker informs me that twenty-
five species of Alg£e are common to New Zealand and to Europe,
but have not been found in the intermediate tropical seas.

From the foregoing facts, namely, the presence of temperate forms
on the highlands across the whole of equatorial Africa, and along
the Peninsula of India, to Ceylon and the Malay Archipelago, and
in a less well-marked manner across the wide expanse of tropical
South America, it appears almost certain that at some former
period, no doubt during the most severe part of a Glacial period,
the lowlands of these great continents were everj'-where tenanted
ander the equator by a considerable number of temperate forms.
At this period the equatorial climate at the level of the sea was
probably about the same with that now experienced at the height
of from five to six thousand feet under the same latitude, or
perhaps even rather cooler. During this, the coldest period, the
lowlands under the equator must have been clothed with a mingled
tropical and temperate vegetation, like that described by Hooker as
growing luxuriantly at the height of from four to five thousand feet
on the lower slopes of the Himalaya, but with perhaps a still
greater preponderance of temperate forms. So again in the moun-
tainous island of Fernando Po, in the Gulf of Guinea, Mr. Mann
found temperate European forms beginning to appear at the height
of about five thousand feet. On the mountains of Panama, at the
height of only two thousand feet. Dr. Seemann found the vegetation
like that of Mexico, " with forms of the torrid zone harmoniously
blended with those of the temperate."

Now let us see whether Mr. Croll's conclusion that when the
northern hemisphere suffered from the extreme cold of the great
Glacial period, the southern hemisphere was actually warmer, throws

Chip. XII.] IN THE NORTH AJ^D SOUTH. 339

any clear light on the present apparently inexplicable distribution of
various organisms in the temperate parts of both hemispheres, and on
the mountains . of the tropics. The Glacial period, as measured by
years, must have been very long ; and when we remember over what
vast spaces some naturalised plants and animals have spread within
a few centuries, this period will have been ample for any amount of
migration. As the cold became more and more intense, we know
that Arctic forms invaded the temperate regions; and, from the
iacts just given, there can hardly be a doubt that some of the more
vigorous, dominant and widest-spreading temperate forms invaded
the equatorial lowlands. The inhabitants of these hot lowlands
would at the same time have migrated to the tropical and sub-
tropical regions of the south, for the southern hemisphere was at this
period warmer. On the decline of the Glacial period, as both hemi-
spheres gradually recovered their former temperatures, the northern
temperate forms living on the lowlands under the equator, would
have been driven to their former homes or have been destroyed,
being replaced by the equatorial forms returning from the south.
Some, however, of the northern temperate forms would almost
certainly have ascended any adjoining high land, where, if suflB-
ciently lofty, they would have long survived like the Arctic forms
on the mountains of Europe. They might have survived, even if
the climate was not perfectly fitted for them, for the change of tem-
perature must have been very slow, and plants undoubtedly possess a
certain capacity for acclimatisation, as shown by their transmitting to
their offspring different constitutional powers of resisting heat and cold.
In the regular course of events the southern hemisphere would in
its turn be subjected to a severe Glacial period, with the northern
hemisphere rendered warmer ; and then the southern temperate
forms would invade the equatorial lowlands. The northern forms
which had before been left on the mountains would now descend
and mingle with the southern forms. These latter, when the
warmth returned, would return to their former homes, leaving some
few species on the mountains, and carrying southward with them
some of the northern temperate forms which had descended from
their mountain fastnesses. Thus, we should have some few species
identically the same in the northern and southern temperate zones
and on the mountains of the intermediate tropical regions. But
the species left during a long time on these mountains, or in opposite
hemispheres, would have to compete with many new forms and
would be exposed to somewhat different physical conditions ; hence
they would be eminently liable to modification, and would generally
now exist as varieties cr as representative species ; and this is the

z 2

340 ALTERNATE GLACIAL PERIODS [Chap. XIL

case. We must, also, bear in mind the occurrence in both hemi-
spheres of former Glacial periods ; for these will accoimt. in
accordance with the same principles, for the many quite distinct
species inhabiting the same widely separated areas, and belonging to
genera not now found in the intermediate torrid zones.

It is a remarkable fact stronf^ly insisted on by Hooker in regard
to America, and by Alph. de Candolle in regard to Australia, that
many more identical or slightly modified species have migrated from
the north to the south, than in a reversed direction. We see,
however, a few southern forms on the mountains of Borneo and
Abyssinia. I suspect that this preponderant migration from the
north to the south is due to the greater extent of land in the north,
and to the northern forms having existed in their own homes in
greater numbers, and having consequently been advanced through
natural selection and competition to a higher stage of perfection, or
dominating power, than the southern forms. And thus, when the
two sets became commingled in the equatorial regions, during
the alternations of the Glacial periods, the northern forms were the
more powerful and were able to hold their places on the mountains,
and afterwards to migrate southward with the southern forms ; but
not so the southern in regard to the northern forms. In the
same manner at the present day, we see that very many European
productions cover the ground in La Plata, New Zealand, and to a
lesser degree in Australia, and have beaten the natives ; whereas
extremely few southern forms have become naturalised in any part
of the northern hemisphere, though hides, wool, and other objects
likely to carry seeds have been largely imported into Eui-ope during
the last two or three centuries from La Plata, and during the last
forty or fifty years from Australia. The Neilgherrie mountains in
India, however, offer a partial exception ; for here, as I hear from
Dr. Hooker, Australian forms are rapidly sowing themselves and
becoming naturalised. Before the last great Glacial period, no
doubt the intertropical mountains were stocked with endemic Alpine
forms ; but these have almost everywhere yielded to the more
dominant forms, generated in the larger areas and more efficient
workshops of the north. In many islands the native productions
are nearly equalled, or even outnumbered, by those which have
become naturalised ; and this is the first stage towards their
extinction. Mountains are islands on the land, and their inhabi-
tants have yielded to those produced within the larger areas of the
north, just in the same way as the inhabitants of real islands have
everywhere yielded and are still yielding to continental forms
naturalised through man's agency.

Chap. XII.] IN THE NORTH AND SOUTH. 341

The same principles apply to the di'Stribution of terresi.rial
animals and of marine productions, in the northern and southern
temperate zones, and on the intertropical mountains. "When,
during the height of the Glacial period, the ocean-currents were
widely different to what they now are, some of tlie inhabitants of
the temperate seas might have reached the equator ; of these a few
would perhaps at once be able to migrate southward, by keeping to
the cooler currents, whilst others might remain and survive in the
colder depths until the southern hemisphere was in its turn sub-
jected to a glacial climate and permitted their further progress ; in
nearly the same manner as, according to Forbes, isolated spaces
inhabited by Arctic productions exist to the present day in the
deeper parts of the northern temperate seas.

I am far from supposing that all the difficulties in regard to th3
distribution and affinities of the identical and allied species, which
now live so widely separated in the north and south, and sometimes
on the intermediate mountain-ranges, are removed on the viev/s
above given. The exact lines of migration cannot be indicated.
We cannot say why certain species and not others have migrated ;
why certain species have been modified and have given rise to new
forms, whilst others have remained unaltered. We cannot hope
to explain such facts, until we can say why one species and not
another becomes naturalised by man's agency in a foreign land ;
why one species ranges twice or thrice as far, and is twice or thrice
as common, as another species wnthin their own homes.

Various special difficulties also remain to be solved ; for instance,
the cccurrence, as shown by Dr. Hooker, of the same plants at points
so enormously remote as Kerguelen Land, New Zealand, and Fuegia ;
but icebergs, as suggested by Lyell, may have been concerned in
their dispersal. 1'he existence at these and other distant points of
ih-^ southern hemisphere, of species, which, though distinct, belong
to genera exclusively confined to the south, is a more remarkable
case. Some of these species are so distinct, that we cannot sup-
pose that there has been time since the commencement of the last
Glacial period for their migration and subsequent modification
10 the necessary degree. The facts seem to indicate that distinct
species belonging to the same genera have migrated in radiating
lines from a common centre; and I am inclined to look in the
southern, as in the northern hemisphere, to a former and warmer
period, before the commencement of the last Glacial period, when
the Antarctic lands, now covered with ice, supported a highly
peculiar and isolated flora. It may be suspected that before this flora
ivas exterminated during the last Glacial epoch, a few forms had

342 ALTERNATE GLACIAL PERIODS. [Chap. XII.

been already widely dispersed to various points of the southern hemi-
sphere by occasional means of transport, and by the aid as halting-
places, of now sunken islands. Thus the southern shores of America,
Australia, and New Zealand, may have become slightly tinted by
the same peculiar forms of life.

Sir C. Lyell in a striking passage has speculated, in language
almost identical with mine, on the effects of great alternations of
climate throughout the world on geographical distribution. And
we have now^ seen that Mr. Croll's conclusion that successive Glacial
periods in the one hemisphere coincide with warmer periods in the
opposite hemisphere, together with the admission of the slow modifi-
cation of species, explains a multitude of facts in the distribution of
the same and of the allied forms of life in all parts of the globe. The
living waters have flowed during one period from the north and
during another from the south, and in both cases have reached the
equator : but the stream of life has flowed with greater force from
the north than in the opposite direction, and has consequently more
freely inundated the south. As the tide leaves its drift in hori-
zontal lines, rising higher on the shores where the tide rises highest,
so have the living waters left their living drift on our mountain
summits, in a line gently rising from the Arctic lowlands to a great
altitude under the equator. The various beings thus left stranded
may be compared with savage races of man, driven up and surviving
ill the mountain fastnesses of almost every land, which serve as a
record, full of interest to us, of the foimer inhabitants of tLs
sun-oundmg lowlands.

Chap. XIII.] FRESH- WATER PRODUCTIONS. 343

CHAPTEE XIII.

Geographical Distribution — continued.

Distribution of fresh-water productions — On the inhabitants of oceanic
islands — Absence of Batrachians and of terrestrial Mammals — On the
relation of the inhabitants of islands to those of the nearest mainland —
On colonisation from the nearest source with subsequent modification
— Summary of the last and present chapter.

Fresh-water Productions.

As lakes and river-systems are separated from each other by barriers
of land, it might have been thought that fresh-water productions
would not have ranged widely within the same country, and as the
sea is apparently a still more formidable barrier, that they would
never have extended to distant countries. But the case is exactly
the reverse. Not only have many fresh- water species, belonging to
different classes, an enormous range, but allied species prevail in a
remarkable manner throughout the world. When first collecting
in the fresh waters of Brazil, I well remember feeling much sur-
prise at the similarity of the fresh-water insects, shells, &c., and
at the dissimilarity of the surrounding terrestrial beings, compared
with those of Britain.

But the wide ranging power of fresh-water productions can, I
think, in most cases be explained by their having become fitted, in
a manner highly useful to them, for short and frequent migrations
from pond to pond, or from stream to stream within their own
countries; and liability to wide dispersal would follow from this
capacity as an almost necessary consequence. We can here consider
only a few cases ; of these, some of the most difficult to explain
arc presented by fish. It was formerly believed that the same
fresh-water species never existed on two continents distant from
each other. But Dr. Giinther has lately shown that the Galaxias
attenuatus inhabits Tasmania, New Zealand, the Falkland Islands,
and the mainland of South America. This is a wonderful case, and
probably indicates dispersal from an Antarctic centre during a former
Warm period. This case, however, is rendered in some degree less

344 FRESH-WATER PRODUCTIONS. [Chap. XIU

surprising by tlie species of this genus having the power of crossing
hy some unknown means considerable spaces of open ocean : thus
tli(!rc is one species common to New Zealand and to the Auckland
Islands, though separated by a distance of about 230 miles. On
the same continent fiesh- water fish often range widely, and as if
c^pi'iciously ; for in two adjoining river-systems some of the species
may be the same, and some wholly ditlerent. It is probable that
they are occasionally transported by what may be called accidental
means. Thus fishes still alive are not very rarely dropped at distant
points by whirlwinds ; and it is known that the ova retain their
vit,ality for a considerable time after removal from the water.
Their dispersal may, however, be mainly attributed to changes in
the level of the land within the recent period, causing rivers to flow
into each other. Instances, also, could be given of this having
occurred during floods, without any change of leveL The wide
difference of the fish on the opposite sides of most mountain-ranges,
which are continuous, and which consequently must from an early
period have completely jireveiited the inosculation of the river-
systems on the two sides, leads to the same conclusion. Some
fresh-water fish belong to very ancient forms, and in such cases
there will have been ample time for great geographical changes, and
consequently time and means for much migration. Moreover Dr.
Giinther has recently been led by several considerations to infer
that with fishes the s:ime forms have a long endurance. Salt-water
fish can with care be slowly accustomed to live in fresh water ;
and, according to Valenciennes, there is hardly a single group ot
which all the members are confined to fresh water, so that a marine
species belonging to a fresh-water group might travel far along the
shores of the sea, and could, it is probable, become adapted without
much difficulty to the fresh waters of a distant land.

Some species of fresh-water shells have very wide ranges, and
allied species which, on our theory, are descended from a common
parent, and must have proceeded from a single source, prevail
throughout the world. ^Jlieir distribution at first perplexed me
much, as their ova are not likely to be transported by birds ; and
the ova, as well as the adults, are immediately killed by sea-water.
I could not even understand how some naturalised species have
spread rapidly throughout the same country. But two facts, which
I have observed — and many others no doubt will be discovered —
throw some light on this subject. When ducks suddenly emerge
from a pond covered with duck-weed, I have twice seen these little
plants adhering to their backs ; and it has happened to me, in
removing a little duck-weed from one aquarium to a nether, that 1

Chap, XIIL] FRESH-WATER PRODUCTIONS. 345

have umntentionally stocked the one with fresh-water shells from
the other. But another agency is perhaps more effectual : I sus-
pended the feet of a duck in an aquarium, where many ova of fresh-
water shells w^ere hatching; and I found that numbers of the
extremely minute and just-hatched shells crawled on the feet, and
clung to them so firmly that when taken out of the water they
could not be jarred off, though at a somewhat more advanced age
they would voluntarily drop off. I'hese just-hatched molluscs,
though aquatic in their nature, survived on the duck's feet, in
damp air, from twelve to twenty hours ; and in this length of time
a duck or heron might fly at least six or seven hundred miles, and
if blown across the sea to an oceanic island, or to any other distant
point, would be sure to alight on a pool or rivulet. Sir Charlea
Lyell informs me that a Dytiscus has been caught with an Ancylus
(a fresh-water shell like a limpet) firmly adhering to it ; and a
water-beetle of the same family, a Colymb6tes, once flew on board
the ' Beagle,' when forty-five miles distant from the nearest land ;
how much farther it might have been blown by a favouring gale
no one can tell.

With respect to plants, it has long been known what enormous
ranges many fresh-water, and even marsh species, have, both over
continents and to the most remote oceanic islands. This is strikingly
illustrated, according to Alph. de Candoiie, in those large groups of
terrestrial plants, w^iich have very few aquatic members ; for the
latter seem immediately to acquire, as if in consequence, a wide
range. I think favourable means of dispersal explain this fact. I
have before mentioned that earth occasionally adheres in some
quantity to the feet and beaks of birds, ^\'ading birds, which fre-
quent the muddy edges of ponds, if suddenly flushed, would be the
most likely to have muddy feet. Birds of this order wander more
than those of any other ; and they are occasionally found on the
most remote and barren islands of the open ocean ; they would not
be likely to alight on the surface of the sea, so that any dirt on
their feet would not be washed of; and when gaining the land,
they would be sure to fly to their natural fresh- water haunts. I do
not believe that botanists are aware how charged the mud of ponds
is with seeds ; I have tried several little experiments, but will here
give only the most striking case : I took in February three table-
spoonfuls of mud from three different points, beneath water, on the
edge of a little pond : this mud when dried weighed only 61 ounces ;
1 kept it covered up in my study for six months, pulling up and
counting each plant as it grew ; the plants were of many kinds,
and were altogether 537 in number ; and yet the viscid mud was all

346 FRESH-WATER PRODUCnOXS. [Chap, XIU

contained in a breakfast cup ! Considering these facts, I think it
would be an inexplicable circumstance if water-birds did not trans-
port the seeds of fresh-water plants to unstockcd ponds and streams,
situated at very distant points. The same agency may have come
into play with the eggs of some of the smaller fresh-water animals.

Other and unknown agencies probably have also played a part.
I have stated that fresh-water fish eat some kinds of seeds, though
they reject many other kinds after having swallowed them ; even
small fish swallow seeds of moderate size, as of the yellow water-
lily and Potamogeton. Herons and other birds, century after cen-
tury, have gone on daily devouring fish ; they then take flight and
go to other waters, or are blown across the sea ; and we have seen
that seeds retain their power of germination, when rejected many
hours afterwards in pellets or in the excrement. When I saw the
great size of the seeds of that fine water-lily, the Nelumbium, and
remembered Alph. de Candolle's remarks on the distribution of
this plant, I thought that the means of its dispersal must remain
inexplicable ; but Audubon states that he found the seeds of the
great southern water-lily (probably, according to Dr. Hooker, the
Kelumbium luteum) in a heron's stomach. Now this bird must
often have flown with its stomach thus well stocked to distant
ponds, and then getting a hearty meal of fish, analogy makes me
believe that it would have rejected the seeds in a pellet in a fit state
for germination.

In considering these several means of distribution, it should be
remembered that when a pond or stream is first formed, for instance,
on a rising islet, it will be unoccupied ; and a single seed or egg
will have a good chance of succeeding. Although there will always
be a struggle for life between the inhabitants of the same pond,
however few in kind, yet as the number even in a well-stocked pond
is small in comparison with the number of species inhabiting an
equal area of land, the competition between them will probably be
less severe than between terrestrial species; consequently an in-
truder from the waters of a foreign country would have a better
chance of seizing on a new place, than in the case of terrestrial
colonists. We should also remember that many fresh-water pro-
ductions are low in the scale of nature, and we have reason to
believe that such beings become modified more slowly than the
high ; and this will give time for the migration of aquatic species.
We should not forget the probability of many fresh-water forms
having formerly ranged continuously over immense areas, and then
having become extinct at intermediate points. But the wide dis-
tribution of fresh-water plants and of the lower animals, whether

Chap. XIIL] INHABITANTS OF OCEANIC ISLANDS. 347

retaining the same identical form or in some degree modified, appa-
rently depends in main part on the wide dispersal of their seeds
and eggs by animals, more especially by fresh-water birds, which
have great powers of flight, and naturally travel from one piece of
"vrater to another.

On tJie Inhabitants of Oceanic Islands.

We now come to the last of the three classes of facts, which 1
have selected as presenting the greatest amount of difficulty with
respect to distribution, on the view that not only all the individuals
of the same species have migrated from some one area, but that
allied species, although now inhabiting the most distant points,
have proceeded from a single area, — the birthplace of their early
progenitors. I have already given my reasons for disbelieving in
continental extensions wnthin the period of existing species, on so
enonnous a scale that all the many islands of the several oceans
were thus stocked with their present terrestrial inhabitants. This
view removes many difficulties, but it does not accord with all the
facts in regard to the productions of islands. In the following
remarks I shall not confine myself to the mere question of dispersal,
but shall consider some other cases bearing on the truth of the two
theories of independent creation and of descent with modification.

The species of all kinds which inhabit oceanic islands are few in
number compared with those on equal continental ai'eas: Alph. de
Candolle admits this for plants, and WoUaston for insects. New
Zealand, for instance, with its lofty mountains and diversified
stations, extending over 780 miles of latitude, together with the
outlying islands of Auckland, Campbell and Chatham, contain
altogether only 960 kinds of flowering plants ; if we compare this
moderate number with the species which swarm over equal areas in
South-Western Australia or at the Cape of Good Hope, we must
admit that some cause, independently of different physical con-
ditions, has given rise to so great a difference in number. Even
the uniform county of Cambridge has 847 plants, and the little
island of Anglesea 764, but a few ferns and a few introduced
plants are included in these numbers, and the comparison in some
other respects is not quite fair. We have evidence that the barren
island of Ascension aboriginally possessed less than half-a-dozen
flowering plants ; yet many species have now become naturalised
on it, as they have in Xew Zealand and on every other oceanic island
which can be named. In St. Helena there is reason to believe that
the naturalised plants and animals have nearly or quite exter-
miual[.3d many native productions. He who admits the doctrine

348 INHABITANTS OF OCEANIC ISLANDS. [Chap. XIIL

of the creation of each separate species, will have to admit that
a sufficient number of the best adapted plants and animals were
not created for oceanic islands ; for man has unintentionally stocked
them far more fully and perfectly than did nature.
^ Although in oceanic islands the species are few in number, the
proportion of endemic kinds {i. e. those found nowhere else in
the world) is often extremely large. If we compare, for instance,
the number of endemic land-shells in Madeira, or of endemic birds
in the Galapagos Archipelago, with the number found on any
coutinent, and then compare the area of the island with that of
the continent, w^e shall see that this is true. This fact might
have been theoretically expected, for, as already explained, species
occasionally arriving after long intervals of time in a new and
isolated district, and having to compete with new associates, would
be eminently liable to modification, and would often produce groups
of modified descendants., But it by no means follows that, because
in an island nearly all the species of one class are peculiar, those of
another class, or of another section of the same class, are peculiar;
and this difference seems to depend partly on the species which are
not modified having immigrated in a body, so that their mutual
relations have not been much disturbed ; and partly on the fre-
quent arrival of unmodified immigrants from the mother-country,
with which the insular forms have intercrossed. It should be
borne in mind that the oS'spring of such crosses would certainly
gain in vigour; so that even an occasional cross would produce
more effect than might have been anticipated. I will give a few
illustrations of the foregoing remarks : in the Galapagos Islands
there are 26 land-birds ; of these 21 (or perhaps 23) are peculiar,
whereas of the 11 marine birds only 2 are peculiar; and it is
obvious that marine birds could arrive at these islands much more
easily and frequently than land-birds. Bermuda, on the other
hand, which lies at about the same distance from North America
as the Galapagos Islands do from South America, and which has
a very peculiar soil, does not possess a single endemic land-bird;
and we know from Mr. J. M, Jones's admirable account of Bermuda,
that very many North American birds occasionally or even fre-
quently visit this island. Almost every j'-ear, as I am informed
by Mr. E. V. Harcourt, many European and African birds are
blown to Madeira ; this island is inhabited by 99 kinds, of which
one alone is peculiar, though very closely related to a European
form; and three or four other species are confined to this island
and ti) the Canaries. So that the Islands of Bermuda and Madeira
have been stocked from the neighbouring continents with birds,

Chap. XIII.1 INHABITANTS OF OCEANIC ISLANDS. 349

which for long ages have there struggled together, and liavo
become mutually co-adapted. Hence when settled in their new
homes, each kind will have been kept by the others to its proper
place and habits, and will consequently have been but little liable
to modification. Any tendency to modification will also have been
checked by intercrossing with the unmodified immigrants, often
arriving from the mother-country. Madeira again is inhabited
by a wonderful number of peculiar land-shells, whereas not one
species of sea- shell is peculiar to its shores : now, though we do
not know how sea-shells are dispersed, yet we can see that their
eggs or larva?, perhaps attached to seaweed or floating timber, or to
the feet of wading-bivds, might be transported across three or four
hundred miles of open sea far more easily than land-shells. The
different orders of insects inhabiting Madeira present nearly paralle*
cases.

/ Oceanic islands are sometimes deficient in animals of certain
whole classes, and their places are occupied by other classes : thus
in the Galapagos Islands reptiles, and in New Zealand gigantic
wingless birds, take, or recently took, the place of mammals.
Although New Zealand is here spoken of as an oceanic island,
it is in some degree doubtful whether it should be so ranked ; it
is of large size, and i-s not separated from Australia by a profoundly
deep sea ; from its geological character and the direction of its
mountain-ranges, the Eev. W. B. Clarke has lately maintained
that this island, as well as New Caledonia, should be ccnsideied as
appurtenances of Australia. Turning to plants, Dr. Hooker has
shown that in the Galapngos Islands the proportional numbers of
the different orders are very different from what they are elsewhere.
All such differences in number, and the absence of certain whole
groups of animals and plants, are generally accounted for by sup-
posed differences in the physical conditions of the islands ; but this
explanation is not a little doubtful;/ Facility of immigration
seems to have been fully as important as the nature of the con-
ditions.

Many remarkable little facts could be given with respect to the
inhabitants of oceanic islands. For instance, in certain islands not
tenanted by a single mammal, some of the endemic plants have
beautifully hooked seeds; yet few relations are more manifest
than that hooks serve for the transportal of seeds in the wool
or fur of quadrupeds. But a hooked seed might be carried to
an island by other means ; and the plant then becoming modified
would form an endemic species, still retaining its hooks, which
would form a useless appendage like the shrivelled wings under

350 ABSENCE OF TERRESTRIAL MAMMALS [Chap. XIIL

the soldered wing-covers of many insular beetles. Again, islands
often possess trees or bushes belonging to orders which elsewhere
include only herbaceous species ; now trees, as Alph. de Candolle
has shown, generally have, whatever the cause may be, confined
ranges. Hence trees would be little likely to reach distant oceanic
islands ; and an herbaceous plant, which had no chance of success-
fully competing with the many fully developed trees growing on
a continent, might, when established on an island, gain an advan-
tage over other herbaceous plants by growing taller and taller and
overtopping them. In this case, natural selection would tend to
add to the stature of the plant, to whatever order it belonged, and
thus first convert it into a bush and then into a tree.

Absence of Batracliians and Terrestrial Mammals on Oceanic

Islands.

With respect to the absence of whole orders of animals on oceanic
islands, Bory St. Vincent long ago remarked that Batrachians
(frogs, toads, newts) are never found on any of the many islands
with which the great oceans are studded. I have taken pains to
verify this assertion, and have found it true, with the exception
of New Zealand, New Caledonia, the Andaman Islands, and per-
haps the Salomon Islands and the Seychelles. But I have already
remarked that it is doubtful whether New Zealand and New Cale-
donia ought to be classed as oceanic islands ; and this is still more
doubtful with respect to the Andaman and Salomon groups and
the Seychelles. This general absence of frogs, toads, and newts on
so many true oceanic islands cannot be accounted for by their
physical conditions : indeed it seems that islands are peculiarly
fitted for these animals ; for frogs have been introduced into Ma-
deira, the Azores, and Mauritius, and have multiplied so as to
become a nuisance. But as these animals and their spawn are im-
mediately killed (with the exception, as far as known, of one Indian
species) by sea- water, there would be great difficulty in their trans-
portal across the sea, and therefore we can see why they do not
exist on strictly oceanic islands. But why, on the theory of crea-
tion, they should not have been created there, it would be very
difficult to explain.

Mammals offer another and similar case. I have carefully searched
the oldest voyages, and have not found a single instance, free from
doubt, of a terrestrial mammal (excluding domesticated animals
kept by the natives) inhabiting an island situated above 300 miles
from a continent or great continental island; and many islands
situated at a much less distance are equally barreu The Falkland

Chap. Xill.] ON OCEANIC ISLANDS. 351

Islands, which are inhabited by a wolf-like fox, Gome nearest to an
exception ; but this group cannot be considered as oceanic, as it
lies on a bank in connection with the mainland at the distance of
about 280 miles ; moreover, icebergs formerly brought boulders to
its western shores, and they may have formerly transported foxes,
as now frequently happens in the arctic regions. Yet it cannot be
said that small islands will not support at least small mammals,
for they occur in many parts of the world on very small islands,
when lying close to a continent ; and hardly an island can be
named on which our smaller quadrupeds have not become natu-
ralised and greatly multiplied. It cannot be said, on the ordinary
viev\ of creation, that there has not been time for the creation of
mammals ; many volcanic islands are sufficiently ancient, as shown
by the stupendous degradation which they have suffered, and by
their tertiary strata : there has also been time for the production
of endemic species belonging to other classes ; and on continents
it is known that new species of mammals appear and disappear at
a quicker rate than other and lower animals. Although terrestrial
mammals do not occur on oceanic islands, aerial mammals do occur
on almost every island. New Zealand possesses two bats found
nowhere else in the world : Norfolk Island, the Viti Archipelago,
the Bonin Islands, the Caroline and Marianne Archipelagoes, and
Mauritius, all possess their peculiar bats. Why, it may be asked,
has the supposed creative force produced bats and no other mam-
mals on remote islands ? On my view this question can easily be
answered ; for no terrestrial mammal can be transported across a
wide space of sea, but bats can fly across. Bats have been seen
wandering by day far over the Atlantic Ocean ; and two North
American species either regularly or occasionally visit Bermuda, at
the distance of 600 miles from the mainland. I hear from Mr.
Tomes, who has specially studied this family, that many species
have enormous ranges, and are found on continents and on far
distant islands. Hence we have only to suppose that such wan-
dering species have been modified in their new homes in relation
to their new position, and we can understand the presence of
endemic bats on oceanic islands, with the absence of all other
terrestrial mammals.

Another interesting relation exists, namely between the depth
of the sea separating islands from each other or from the nearest
continent, and the degree of affinity of their mammalian inha-
bitants. Mr. Windsor Earl has made some striking observations
ou this head, since greatly extended by Mr. Wallace's admirable
researches, in regard to the great Malay Archipelago, which is

352 ABSExXCE OF TERRESTKIAL MAMMt^LS [Chap. XIII.

traversed near Celebes by a space of deep ocean, and i\\s separate*
two widely distinct mammalian faunas. On either side the islands
stand on a moderately shallow submarine bank, and these islands
are inhabited by the same or by closely allied quadrupeds. I have
not as yet had time to follow up this subject in all quarters of the
world; but as far as I have gone, the relation holds good. For
instance, Britain is separated by a shallow channel from Europe,
and the mammals are the same on both sides ; and so it is with all
the islands near the shores of Australia. The West Indian Islands,
on the other hand, stand on a deeply submerged bank, nearly 1000
fathoms in depth, and here we find American forms, but the species
and even the genera are quite distinct. As the amount of modi-
fication which animals of all kinds undergo, partly depends on the
lapse of time, and as the islands which are separated from each
other or from the mainland by shallow channels, are more likely
to have been continuously united within a recent period than the
islands separated by deeper channels, we can understand how it
is that a relation exists between the depth of the sea separating
two mammalian faunas, and the degree of their affinity, — a relation
which is quite inexplicable on the theory of independent acts of
creation.

The foregoing statements in regard to the inhabitants of oceanic
islands, — namely, the fewness of the species, with a large proportion
consisting of endemic forms — the members of certain groups, but
not those of other groups in the same class, having been modified —
the absence of certain whole orders, as of batrachians and of ter-
restrial mammals, notwithstanding the presence of aerial bats, —
the singular proportions of certain orders of plants, — herbaceous
forms having been developed into trees, &c., — seem to me to accord
better with the belief in the efficiency of occasional means of trans-
port, carried on during a long course of time, than with the belief
in the former connection of all oceanic iblands with the nearest
continent ; for on this latter view it is probable that the various
classes would have immigrated more uniformly, and from the
species having entered in a body their mutual relations would not
have been much disturbed, and consequently they would either have
not been modified, or all the species in a more equable manner.

I do not deny that there are many and serious difiiculties in
understanding how many of the inhabitants of the more remote
islands, whether still retaining the same specific form or subse-
quently modified, have reached their present homes. But the
probability of other islands having once existed as halting-places,
of which not a wreck now remains, must not be overlooked. I will

Chap. XIIL] ON OCEANIC ISLANDS. 353

specify one difficult case. Almost all oceanic islands, even the
most isolated and smallest, are inhabited by land-shells, generally
by endemic species, but sometimes by species found elsewhere, —
striking instances of which have been given by Dr. A. A. Gould
in relation to the Pacific. Now it is notorious that land-shells
are easily killed by sea-water ; their eggs, at least such as I have
tried, sink in it and are killed. Yet there must be some unknown,
but occasionally efficient means for their transportal. Would the
just-hatched young sometimes adhere to the feet of birds roosting
on the ground, and thus get transported ? It occurred to me that
land-shells, when hybernating and having a membranous diaphragm
over the mouth of the shell, might be floated in chinks of drifted
timber across moderately wide arms of the sea. And I find that
several species in this state withstand uninjured an immersion in
sea-water during seven days : one shell, the Helix pomatia, after
having been thus treated and again hybernating was put into sea-
water for twenty days, and perfectly recovered. During this length
of time the shell might have been carried by a marine current of
average swiftness, to a distance of 660 geographical miles. As
this H'ilix has a thick calcareous operculum, I removed it, and
when it had formed a new membranous one, I again immersed it
for fourteen days in sea-water, and again it recovered and crawled
away. Baron Aucapitaine has since tried similar experiments : he
placed 100 land-shells, belonging to ten species, in a box pierced
with holes, and immersed it for a fortnight in the sea. Out of the
hundred shells, twenty-seven recovered. The presence of an oper-
culum seems to have been of importance, as out of twelve specimens
of Cyclostoma elegans, which is thus furnished, eleven revived. It
is remarkable, seeing how well the Helix pomatia resisted with me
the salt-water, that not one of fifty-four specimens belonging to
four other species of Helix tried by Aucapitaine, recovered. It is,
however, not at all probable that land-shells have often been thus
transported ; the feet of birds offer a more probable method.

On the Relations of the Inhabitants of Islands to those of the
nearest Mainland.

The most striking and important fact for us is the affinity of the
species which inhabit islands to those of the nearest mainland,
without being actually the same. Numerous instances could be
given. The Galapagos Archipelago, situated under the equator,
lies at the distance of between 500 and 600 miles from the shores
of South America. Here almost every product of the land and oi
the water bears the unmistakeable stamp of the American continent*

2 A

354 RELATIONS OF THE INHABITANTS OF [Chap. XIII.

There are twenty-six land-birds ; of these, twenty-one or perhaps
twenty-three are ranked as distinct species, and would commonly be
assumed to have been here created ; yet the close afifinity of most
of these birds to American species is manifest in every character,
in their habits, gestures, and tones of voice. So it is with the other
animals, and with a large proportion of the plants, as shown by
Dr. Hooker in his admirable Flora of this archipelago. The natu-
ralist, looking at the inhabitants of these volcanic islands in the
Pacific, distant several hundred miles from the continent, feels that
he is standing on American land. Why should this be so ? why
should the species which are supposed to have been created in
the Galapagos Archipelago, and nowhere else, bear so plainly the
stamp of affinity to those created in America ? There is nothing
in the conditions of life, in the geological nature of the islands, in
their height or climate, or in the proportions in which the several
classes are associated together, which closely resembles the con-
ditions of the South American coast : in fact, there is a consider-
able dissimilarity in all these respects. On the other hand, there
is a considerable degree of resemblance in the volcanic nature of
the soil, in the climate, height, and size of the islands, between the
Galapagos and Cape Yerde Archipelagoes : but what an entire
and absolute difference in their inhabitants ! The inhabitants of
the Cape Verde Islands are related to those of Africa, like those
of the Galapagos to America. • Facts such as these, admit of no
sort of explanation on the ordinary view of independent creation ;
whereas on^he view here maintained, it is obvious that the Gala-
pagos Islands would be likely to receive colonists from America,
whether by occasional means of transport or (though I do not
believe in this doctrine) by formerly continuous land, and the Cape
Verde Islands from Africa ; such colonists would be liable to modi-
fication,— the principle of inheritance still betraying their original
birthplace.

Many analogous facts could be given: indeed it is an almost
universal rule that the endemic productions of islands are related
to those of the nearest continent, or of the nearest large island.
The exceptions are few, and most of them can be explained.
Thus although Kerguelen Land stands nearer to Africa than to
America, the plants are related, and that very closely, as we know
from Dr. Hooker's account, to those of America : but on the view
that this island has been mainly stocked by seeds brought with
earth and stones on icebergs, drifted by the prevailing currents,
this anomaly disappears. New Zealand in its endemic planes is
much more closely related to Australia, the nearest mainland, than

Chap. XIIL] ISLANDS TO THOSE OF THE MAINLAND. 355

to any other region : and this is what might have been expectod ;
but it is also plainly related to South America, which, although
the next nearest continent, is so enormously ren:/ote, that the fact
becomes an anomaly. But this difficulty partially disappears on
the view that New Zealand, South America, and the other southern
lands have been stocked in part from a nearly intermediate though
distant point, namely from the antarctic islands, when they were
clothed with vegetation, during a warmer tertiary period, before the
commencement of the last Glacial period. The affinity, which
though feeble, I am assured by Dr. Hooker is real, between the flora
of the south-western corner of Australia and of the Cape of Good
Hope, is a far more remarkable case ; but this affinity is confined
to the plants, and will, no doubt, some day be explained.

The same law which has determined the relationship between
the inhabitants of islands and the nearest mainland, is sometimes
displayed on a small scale, but in a most interesting manner,
within the limits of the same archipelago. Thus each separate
island of the Galapagos Archipelago is tenanted, and the fact is a
marvellous one, by many distinct species: but these species are
related to each other in a very much closer manner than to the
inhabitants of the American continent, or of any other quarter
of the world. This is what might have been expected, for islands
situated so near to each other would almost necessarily receive im-
migrants from the same original source, and from each other. But
how is it that many of the immigrants have been' differently
modified, though only in a small degree, in islands situated within
sight of each other, having the same geological nature, the same
height, climate, &c. ? This long appeared to me a great difficulty :
but it arises in chief part from the deeply-seated error of considering
the physical conditions of a country as the most important ; whereas
it cannot be disputed that the nature of the other species with
which each has to compete, is at least as important, and generally
a far more important element of success. Now if we look to the
species which inhabit the Galapagos Archipelago and are like-
wise found in other parts of the world, we find that they difi'er
considerably in the several islands. This difference might indeed
have been expected if the islands have been stocked by occasional
means of transport — a seed, for instance, of one plant having been
brought to one island, and that of another plant to another island,
though all proceeding from the same general source. Hence, when
in former times an immigrant first settled on one of the islands,
or when it subsequently spr.ead from one to another, it would
undoubtedly be exposed to different conditions in the diff'erent

2 A 2

856 RELATIONS OF THE INHABITANTS OF [Ckap. XIII.

islands, for it would have to compete with a difierent set of
organisms ; a plant for instance, would find the ground best fitted
for it occupied loj somewhat different species in the difierent
islands^ and would be exposed to the attacks of somewhat dif-
ferent enemies. If then it varied, natural selection would probably
favour diflierent varieties in the different islands. Some species^
however, might spread and yet retain the same character through-
out the group, just as we see some species spreading widely
throughout a continent and remaining the same.

The really surprising fact in this case of the Galapagos Archipe-
lago, and in a lesser degree in some analogous cases, is that each
new species after being formed in any one island, did not spread
quickly to the other islands. But the islands, though in sight of
each other, are separated by deep arms of the sea, in most cases
wider than the British Channel, and there is no reason to suppose
that they have at any former period been continuously united.
The currents of the sea are rapid and sweep between the islands,
and gales of wind are extraordinarily rare ; so that the islands are
far more effectually separated from each other than they appear on
a map. Nevertheless some of the species, both of those found in
other parts of the world and of those confined to the archipelago,
are common to the several islands ; and we may infer from their
present manner of distribution, that they have spread from one
island to the others. But we often take, I think, an erroneous view
of the probability of closely-allied species invading each other's
territory, when put into free intercommunication. Undoubtedly, if
one species has any advantage over another, it will in a very brief
time wholly or in part supplant it ; but if both are equally well fitted
for their own places, both will probably hold their separate places
for almost any length of time. Being familar with the fact that
many species, naturalised through man's agency, have spread with
astonishing rapidity over wide areas, we are apt to infer that most
species would thus spread ; but we should remember that the species
which become naturalised in new countries are not generally closely
allied to the aboriginal inhabitants, but are very distinct forms,
belonging in a large proportion of cases, as shown by Alph. de
Candolle, to distinct genera. In the Galapagos Archipelago, many
even of the birds, though so well adapted for flying from island
to island, differ on the different islands; thus there are three
closely-allied species of mocking- thrush, each confined to its own
island. Now let us suppose the raocking-thrush of Chatham
Island to be blown to Charles Island, which has its own mocking-
thrush ; why should it succeed in establishing itself there ? We

Chap. XIII.] ISLANDS TO THOSE OF THE MAINLAND. 357

may safely infer that Charles Island is well stocked with its own
species, for annually more eggs are laid and young birds hatched,
than can possibly be reared ; and we may infer that the mocking-
thrush peculiar to Charles Island is at least as well fitted for its
home as is the species peculiar to Chatham Island. Sir C. Lyell
and Mr. Wollaston have communicated to me a remarkable fact
bearing on this subject ; namely, that Madeira and the adjoining
islet of Porto Santo possess many distinct but representative
species of land-shells, some of which live in crevices of stone ;
and although large quantities of stone are annually transported
from Porto Santo to Madeira, yet this latter island has not become
colonised by the Porto Santo species; nevertheless both islands
have been colonised by European land-shells, which no doubt had
some advantage over the indigenous species. From these con-
siderations I think we need not greatly marvel at the endemic
species which inhabit the several islands of the Galapagos Archi-
l)elago, not having all spread from island to island. On the same
continent, also, preoccupation has probably played an important
part in checking the commingling of the species which inhabit
different districts with nearly the same physical conditions. Thus,
the south-east and south-west corners of Australia have nearly the
same physical conditions, and are united by continuous land,
yet they are inhabited by a vast number of distinct mammals,
birds, and plants ; so it is, according to Mr. Bates, with the butter-
flies and other animals inhabiting the great, open, and continuous
valley of the Amazons.

The same principle which governs the general character of the
inhabitants of oceanic islands, namely, the relation to the source
whence colonists could have been most easily derived, together with
their subsequent modification, is of the widest application through-
out nature. We see this on every mountain-summit, in every lake
and marsh. For Alpine species, excepting in as far as the same
species have become widely spread during the Glacial epoch, are
related to those of the surrounding lowlands ; thus we have in
South America, Alpine humming-birds, Alpine rodents, Alpine
plants, &c., all strictly belonging to American forms ; and it is
obvious that a mountain, as it became slowly upheaved, would be
oolonised from the surrounding lowlands. So it is with the inha-
bitants of lakes and marshes, excepting in so far as great facility
of transport has allowed the same forms to prevail throughout
large portions of the world. We see this same principle in the
character of most of the blind animals inhabiting the caves of
America and of Europe. Other analogous facts could be given,

S58 RELATIONS OF TEE INHABITANTS OF [^'iiap. Xlli,

It will, I believe, be found universally true, that wherever in two
regions, let them be ever so distant, many closely allied or repre-
sentative species occur, there will likewise be found some identical
species ; and wherever many closely-allied species occur, there will
be found many forms which some naturalists rank as distinct
species, and others as mere varieties ; these doubtful forms showing
us the steps in the progress of modification.

The relation between the power and extent of migration in
certain species, either at the present or at some former period, and
the existence at remote points of the world of closely-allied species,
is shown in another and more general way. Mr. Gould remarked
to me long ago, that in those genera of birds which range over the
world, many of the species have very wide ranges. I can hardly
doubt that this rule is generally true, though difficult of proof.
Amongst mammals, we see it strikingly displayed in Bats, and
in a lesser degree in the Felidse and Canidje. We see the same
rule in the distribution of butterflies and beetles. So it is with
most of the inhabitants of fresh water, for many of the genera
in the most distinct classes range over the world, and many of the
species have enormous ranges. It is not meant that all, but that
some of the species have very wide ranges in the genera which
range very widely. Nor is it meant that the species in such
genera have on an average a very wide range; for this will
largely depend on how far the process of modification has gone ;
for instance, two varieties of the same species inhabit America
and Europe, and thus the species has an immense range ; but, if
variation were to be carried a little further, the two varieties would
be ranked as distinct species, and their range would be greatly
reduced. Still less is it meant, that species which have the
capacity of crossing barriers and ranging widely, as in the case
of certain powerfully- winged birds, will necessarily range widely;
for we should never forget that to range widely implies not only
the power of crossing barriers, but the more important power of
being victorious in distant lands in the struggle for life with
foreign associates. But according to the view that all the species
of a genus, though distributed to the most remote points of the
world, are descended from a single progenitor, we ought to find,
and I believe as a general rule we do find, that some at least of
the species range very widely.

We should bear in mind that many genera in all classes are of
ancient origin, and the species in this case will have had ample
time for dispersal and subsequent modification. There is also
reason to believe from geological evidence, that within each great

Chap. XIII.] ISLANDS TO THOSE OF THE MAINLAND. 359

class the lower organisms change at a slower rate than tlie higher ;
consequently they will have had a better chance of ranging widely
and of still retaining the same specific character. This fact,
together with that of the seeds and eggs of most lowly organised
forms being very minute and better fitted for distant transportal,
probably accounts for a law which has long been observed, and
which has lately been discussed by Alph. de Candollc in regard tc
plants, namely, that the lower any group of organisms stands, the
more widely it ranges.

The relations just discussed, — namely, lower organisms ranging
more widely than the higher, — some of the species of widely-
ranging genera themselves ranging widely, — such facts, as alpine^
lacustrine, and marsh productions being generally related to those
which live on the surrounding low lands and dry lands, — the
striking relationship between the inhabitants of islands and those
of the nearest mainland — the still closer relationship of the distinct
inhabitants of the islands in the same archipelago — are inexplicable
on the ordinary view of the independent creation of each species,
but are explicable if we admit colonisation from the nearest or
readiest source, together with the subsequent adaptation of the
colonists to their new homes.

Summary of the last and present Chapters.

In these chapters I have endeavoured to show, that if we make
due allowance for our ignorance of the full effects of changes of
climate and of the level of the land, which have certainly occurred
within the recent period, and of other changes which have probably
occurred, — if we remember how ignorant we are with respect to the
many curious means of occasional transport, — if we bear in mind,
and this is a very important consideration, how often a species
may have ranged continuously over a wide area, and then have
become extinct in the intermediate tracts, — the difficulty is not
insuperable in believing that all the individuals of the same
species, wherever found, are descended from common parents.
And we are led to this conclusion, which has been arrived at by
many naturalists under the designation of single centres of creation,
by various general considerations, more especially from the import-
ance of barriers of all kinds, and from the analogical distribution ci
sub-genera, genera, and families.

With respect to distinct species belonging to the same genus,
which on our theory have spread from one parent-source ; if we
make the same allowances as before for our ignorance, and re-
member that some forms of life have changed very slowly,

S60 SULOTARY OF THE [Chap XIII.

enormous periods of time having been thus granted for their
migration, the difficulties are far from insuperable; though in
this case, as in that of the individuals of the same species, they
are often great.

As exemplifying the effects of climatal changes on distribution,
I have attempted to show how important a part the last Glacial
XDeriod has played, which affected even the equatorial regions,
and which, during the alternations of the cold in the north and
south, allowed the productions of opposite hemispheres to mingle,
and left some of them stranded on the mountain-summits in all
parts of the world. As showing how diversified are the ^ means
of occasional transport, I have discussed at somo little length the
means of dispersal of fresh-water productions.

If the difficulties be not insuperable in admitting that in the
long course of time all the individuals of the same species, and
likewise of the several species belonging to the same genus, have
proceeded from some one source ; then all the grand leading facts
of geographical distribution are explicable on the theory of
migration, together with subsequent modification and the multipli-
cation of new forms. We can thus understand the high importance
of barriers, whether of land or water, in not only separating, but in
apparently forming the several zoological and botanical provinces.
We can thus understand the concentration of related species within
the same areas ; and how it is that under diff'erent latitudes, for
instance in South America, the inhabitants of the plains and
mountains, of the forests, marshes, and deserts, are linked together
in so mysterious a manner, and are likewise linked to the extinct
beings which formerly inhabited the same continent. Bearing in
mind that the mutual relation of organism to organism is of the
highest importance, we can see why two areas having nearly the
same physical conditions should often be inhabited by very different
forms of life ; for according to the length of time which has elapsed
since the colonists entered one of the regions, or both ; according
to the nature of the cormnunication which allowed certain forms
and not others to enter, either in greater or lesser numbers ; accord-
ing or not, as those which entered happened to come into more or
less direct competition with each other and with the aborigines ;
and according as the immigrants were capable of varying more or
less rapidly, there would ensue in the two oi more regions, inde-
pendently of their physical conditions, infinitely diversified con-
ditions of life, — there would be an almost endless amount of organic
action and reaction, — and we should find some groups of beings
greatly, and some only slightly modified, — some developed in great

Chap. XIII.] LAST AND PRESENT CHAPTERS. 361

force, some existing in scanty numbers — and this we do find ic
the several great geographical provinces of the world.

On these same principles we can tinderstand, as I have endea-
voured to show, why oceanic islands should have few inhabitants,
but that of these, a large proportion should be endemic or peculiar ;
and why, in relation to the means of migration, one group of beings
should have all its species peculiar, and another group, even within
the same class, should have all its species the same with those in
an adjoining quarter of the world. We can see why whole groups
of organisms, as batrachians and terrestrial mammals, should be
absent from oceanic islands, whilst the most isolated islands should
possess their own peculiar species of aerial mammals or bats. We
can see why, in islands, there should be some relation between the
presence of mammals, in a more or less modified condition, and
the depth of the sea between such islands and the mainland. We
can clearly see why all the inhabitants of an archipelago, though
specifically distinct on the several islets, should be closely related
to each other ; and should likewise be related, but less closely, to
those of the nearest continent, or other source whence immigrants
might have been derived. We can see why, if there exist very
closely allied or representative species in two areas, however distant
from each other, some identical species will almost always there be
found.

As the late Edward Forbes often insisted, there is a striking
parallelism in the laws of life throughout time and space ; the laws
governing the succession of forms in past times being nearly th(^
same with those governing at the present time the differences in
different areas. We see this in many facts. The endurance of each
species and group of species is continuous in time ; for the apparent
exceptions to the rule are so few, that they may fairly be attributed
to our not having as yet discovered in an intermediate deposit certain
forms which are absent in it, but which occur both above and
below : so in space, it certainly is the general rule that the area in*
habited by a single species, or by a group of species, is continuous,
and the exceptions, which are not rare, may, as I have attempted
to show, be accounted for by former migrations under different cir-
cumstances, or through occasional means of transport, or by the
species having become extinct in the intermediate tracts. Both
in time and space, species and groups of species have their points
of maximum development. Groups of species, living during the
same period of time, or living within the same area, are often
characterised by trifling features in common, as of sculpture or
colour. In looking to the long succession of past ages, as iii

362 SUMMARY. [Chap. Xia

looking to distant provinces throughout the world, we find that
species in certain classes differ little from oach other, whilst those
in another class, or only in a different section of the same order,
differ greatly from each other. In both time and space the bwly
organised members of each class generally change less than the
highly organised ; but there are in both cases marked exceptions
to the rule. According to our theory, these several relations
throughout time and space are intelligible ; for whether we look to
the allied forms of life which have changed during successive ages,
or to those which have changed after having migrated into distant
quarters, in both cases they are connected by the same bond of
ordinary generation ; in both cases the laws of variation have been
the same, and modifications have been accumulated by the saraa
means of natural selection.

Chap. XIV.l CLASSIFICATION. 3C3

CHAPTEE XIV.

Mutual Affinities of Organic Beings : Morphology :
Embryology : Kudimentary Organs.

Classification, groups subordinate to groups — Natural system — Rules
and difficulties in classification, explained on the theory of descent with
modification — Classification of varieties — Descent always used in
classification — Analogical or adaptive characters — Affinities, general,
complex, and radiating — Extinction separates and defines groups —
Morphology, between members of the same class, between parts of
the same individual — Embryology, laws of, explained by variations
not supervening at an early age, and being inherited at a corresponding
age — Rudimentary organs ; their origin explained — Summary.

Classification.

From tlie most remote period in the history of the world organic
beings have been found to resemble each other in descending de-
grees, so that they can be classed in groups under groups. This
classification is not arbitrary like the grouping of the stars in
constellations. The existence of groups would have been of simple
significance, if one group had been exclusively fitted to inhabit the
land, and another the water ; one to feed on flesh, another on vege-
table matter, and so on ; but the case is widely different, for it is
notorious how commonly members of even the same sub-group have
diflerent habits. In the second and fourth chapters, on Variation
and on Natural Selection, I have attempted to show that v/ithin each
country it is the widely ranging, the much diffused and common,
that is the dominant species, belonging to the larger genera in each
class, which vary most. The varieties, or incipient species, thus
produced, ultimately become converted into new and distinct
species ; and these, on the principle of inheritance, tend to produce
other new and dominant species. Consequently the groups which
are now large, and which generally include many dominant species,
tend to go on increasing in size. I further attempted to show that
from the varying descendants of each species trying to occupy as
many and as different places as possible in the economy of nature,
they constantly tend to diverge in character. This latter conclusion

364 CLASSIFICATION. [Chap. XIV.

is supported by observing the great diversity of forms which, in any
small area, come into the closest competition, and by certain facts
in naturalisation.

I attempted also to show that there is a steady tendency in the
forms which are increasing in number and diverging in character,
to supplant and exterminate the preceding, less divergent and less
improved forms. I request the reader to turn to the diagram
illustrating the action, as formerly explained, of these several
principles ; and he will see that the inevitable result is, that the
modified descendants proceeding from one progenitor become broken
up into groups subordinate to groups. In the diagram each letter
on the uppermost line may represent a genus including several
species ; and the whole of the genera along this upper line form
together one class, for all are descended from one ancient parent
and, consequently, have inherited something in common. But the
three genera on the left hand have, on this same principle, much in
common, and form a sub-family, distinct from that containing the
next two genera on the right hand, which diverged from a common
parent at the fifth stage of descent. These five genera have also
much in common, though less than when grouped in sub-families ;
and they form a family distinct from that containing the three
genera still farther to the right hand, which diverged at an earlier
period. And all these genera, descended from (A), form an order
distinct from the genera descended from (I). So that we here have
many species descended from a single progenitor grouped into
genera ; and the genera into sub-families, families, and orders, all
under one great class. The grand fact of the natural subordination
of organic beings in groups under groups, which, from its famili-
arity, does not always sufficiently strike us, is in my judgment thus
explained. No doubt organic beings, like all other objects, can be
classed in many ways, either artificially by single characters or more
naturally by a number of characters. We know, for instance, that
minerals and the elemental substances can be thus arranged. In
this case there is of course no relation to genealogical succession,
and no cause can at present be assigned for their falling into
groups. But with organic beings the case is different, and the
view above given accords with their natural arrangement in group
under group ; and no other explanation has ever been attempted.

Naturalists, as we have seen, try to arrange the species, genera,
and families in each class, on what is called the Natural System.
But what is meant by this system ? Some authors look at it merely
as a scheme for arranging together those living objects which are
most alike, and for separating those which ai'e most uulike ; or as

Ceap. XIV.] CLASSIFICATION. 365-

an artificial metliod of enunciating, as briefly as possible, general
propositions, — that is, by one sentence to give the characters
common, for instance, to all mammals, by another those common
to all carnivora, by another those common to the dog-genus, and
then, by adding a single sentence, a full description is given of each
kind of dog. The ingenuity and utility of this system are indispu-
table. But many naturalists tnink that something more is meant
by the Natural System ; they believe that it reveals the plan of the
Creator ; but unless it be specified whether order in time or space,
or both, or what else is meant by the plan of the Creator, it seems
to me that nothing is thus added to our knowledge. Expressions
such as that famous one by Linnseus, which we often meet with in
a more or less concealed form, namely, that the characters do not
make the genus, but that the genus gives the characters, seem to
imply that some deeper bond is included in our classifications than
mere resemblance. I believe that this is the case, and that commu-
nity of descent — the one known cause of close similarity in organic
beings — is the bond, which though observed by various degrees of
modification, is partially revealed to us by our classifications.

Let us now consider the rules followed in classification, and the
difficulties which are encountered on the view that classification
either gives some unknown plan of creation, or is simply a scheme
for enunciating general propositions and of placing together the
forms most like each other. It might have been thought (and was
in ancient times thought) that those parts of the structure which
determined the habits of life, and the general place of each being
in the economy of nature, would be of very high importance in
classification. Nothing can be more false. No one regards the
external similarity of a mouse to a shrew, of a dugong to a whale,
of a whale to a fish, as of any importance. These resemblances,
though so intimately connected with the whole life of the beings
are ranked as merely "adaptive or analogical characters ; " but to
the consideration of these resemblances we shall recur. It may
even be given as a general rule, that the less any part of the organ-
isation is concerned with special habits, the more important it
becomes for classification. As an instance : Owen, in speaking of
the dugong, says, " The generative organs, being those which are
most remotely related to the habits and food of an animal, I have
always regarded as affording very clear indications of its true affini-
ties. We are least likely in the modifications of these organs to
mistake a merely adaptive for an essential character." With plants
how remarkable it is that the organs of vegetation, on which their
nutrition and life depend, are of little signification; whereas tha

me CLASSIFICATION. [Ch IIV.

organs of reproduction, ivith their product tlie seed and embryo, are
of paramount importance ! So again in formerly discussing certain
morphological characters which are not functionally important, we
have seen that they are often of the highest service in classification.
This depends on their constancy throughout many allied groups ;
and their constancy chiefly depends on any slight deviations not
having been preserved and accumulated by natural selection, which
acts only on serviceable characters.

That the mere physiological importance of an organ does not
determine its classificatory value, is almost proved by the fact, that
in allied groups, in which the same organ, as we have every reason
to suppose, has nearly the same physiological value, its classificatory
value is widely different. No naturalist can have worked long at
any group without being struck with this fact ; and it has been
fully acknowledged in the writings of almost every author. It
will suffice to quote the highest authority, Kobert Brown, who,
in speaking of certain organs in the Proteacse, says their generic
importance, " like that of all their parts, not only in this, but, as 1
apprehend, in every natural family, is very imequal, and in some
cases seems to be entirely lost." Again, in another work he says,
the genera of the Connaracese " differ in having one or more
ovaria, in the existence or absence of albumen, in the imbricate or
valvular aestivation. Any one of these characters singly is fre-
quently of more than generic importance, though here even when
all taken together they appear insufficient to separate Cnestis from
Connarus," To give an example amongst insects : in one great di-
vision of the Hymenoptera, the antennse, as Westwood has remarked,
are most constant in structure ; in another division they differ much,
and the difierences are of quite subordinate value in classification ;
yet no one will say that the antennse in these two divisions of the
same order are of unequal physiological importance. Any number
of instances could be given of the varying importance for classi-
fication of the same important organ within the same group of
beings.

Again, no one will say that rudimentary or atrophied organs are
of high physiological or vital importance ; yet, undoubtedly, organs
in this condition are often of much value in classification. No one
will dispute that the rudimentary teeth in the upper jaws of young
ruminants, and certain rudimentary bones of the leg, are highly
serviceable in exhibiting the close affinity between ruminants aud "
pachyderms. Robert Brown has strongly insisted on the fact that
the position of the rudimentary florets is of the highest importance
in the classification of the grasses.

Chap. ^ f CLASSIFICATION. 367

Numerous instances could be given of characters derived from
parts whicfi must be considered of very trifling physiological import-
ance, but wliich are universally admitted as highly serviceable in
the definiiibn of whole groups. For instance, whether or not there
is an open passage from the nostrils to the mouth, the only charac-
ter, according to Owen, which absolutely distinguishes fishes and
reptiles — the inflection of the angle of the lower jaw in Marsupials
' — the manner in which the wings of insects are folded — mere
colour in certain Algse — mere pubescence on parts of the flower in
grasses — the nature of the dermal covering, as hair or feathers,
in the Vertebrata. If the Ornithorhynchus had been covered with
feathers instead of hair, this external and trifling character would
have been considered by naturalists as an important aid in deter-
mining the degree of afiinity of this strange creature to birds.

The importance, for classification, of trifling characters, mainly
depends on their being correlated with many other characters of
more or less importance. The value indeed of an aggregate of
characters is very evident in natural history. Hence, as has often
been remarked, a species may depart from its allies in several
characters, both of high physiological importance, and of almost
universal prevalence, and yet leave us in no doubt where it should
be ranked. Hence, also, it has been found that a classification
founded on any single character, however important that may be,
has always failed; for no part of the organisation is invariably
constant. The importance of an aggregate of characters, even when
none are important, alone explains the aphorism enunciated by
Linnasus, namely, that the characters do not give the genus, but
the genus gives the characters; for this seems founded on the
appreciation of many trifling points of resemblance, too slight to be
defined. Certain plants, belonging to the Malpighiacese, bear
perfect and degraded flowers ; in the latter, as A. de Jussieu has
remarked, " the greater number of the characters proper to the
species, to the genus, to the family, to the class, disappear, and thus
laugh at our classification." When Aspicarpa produced in France,
during several years, only these degraded flowers, departing so
wonderfully in a number of the most important points Of structure
[ fj-'-m the proper type of the order, yet M. Eichard sagaciously saw,
r, as -Jussieu observes, that this genus should still be retained amongst
the Malpighiacese. This case well illustrates the spirit of our
classifications.

Practically, when naturalists are at work, they do not trouble
themselves about the physiological value of the characters which
they use in defining a group or in allocating any particular fpecies.

308 CLASSIFICATION. [Chap. XIV.

If they find a character nearly uniform, and common to a great
number of forms, and not common to others, they use it as one of
high value ; if common to some lesser number, they uae it as of
subordinate value. This principle has been broadly confessed by
some naturalists to be the true one ; and by none more clearly than
by that excellent botanist, Aug. St. Hilaire. If several trifling cha-
racters are always found in combination, though no apparent bond
of connection can be discovered between them, especial value is set
on them. As in most groups of animals, important organs, such as
those for propelling the blood, or for aerating it, or those for pro-
pagating the race, are found nearly uniform, they are considered as
highly serviceable in classification ; but in some groups all these,
the most important vital organs, are found to offer characters of
quite subordinate value. Thus, as Fritz Miiller has lately remarked,
in the same group of crustaceans, Cypridina is furnished with a
heart, whilst in two closely allied genera, namely Cypris and
Cytherea, there is no such organ ; one species of Cypridina has well-
developed branchise, whilst another species is destitute of them.

We can see why characters derived from the embryo should be
of equal importance with those derived from the adult, for a natural
classification of course includes all ages. But it is by no means
obvious, on the ordinary view, why the structure of the embryo
should be more important for this purpose than that of the adult,
which alone plays its full part in the economy of nature. Yet it;
has been strongly urged by those great naturalists, Milne Edwards
and Agassiz, that embryological characters are the most important
of all ; and this doctrine has very generally been admitted as true.
Nevertheless, their importance has sometimes been exaggerated,
owing to the adaptive characters of larvae not having been excluded ;
in order to show this, Fritz Miiller arranged by the aid of such
characters alone the great class of crustaceans, and the arrangement
did not prove a natural one. But there can be no doubt that
embryonic, excluding larval characters, are of the highest value
for classification, not only with animals but with plants. Thus the
main divisions of flowering plants are founded on differences in
the embryo, — on the number and position of the cotyledons, and on
the mode of development of the plumule and radicle. We shall
immediately see why these characters possess so high a value in
classification, namely, from the natural system being genealogical
in its arrangement.

Our classifications are often plainly influenced by chains of affini-
ties. Nothing can be easier than to define a number of characters
common to all birds ; but with crustaceans, any such definition has

Chap. XIV.] CLASSIFICATION. 369

hitherto beea found impossible. There are crustaceans at the
opposite ends of the series, which have hardly a character in com-
mon ; yet the species at both ends, from being plainly allied to
others, and these to others, and so onwards, can be recognised as
unequivocally belonging to this, and to no other class of the
Articulata.

Geographical distribution has often been used, though perhaps
not quite logically, in classification, more especially in very large
groups of closely allied forms. Temminck insists on the utility or
even necessity of this practice in certain groups of birds ; and it has
been followed by several entomologists and botanists.

Finally, with respect to the comparative value of the various
groups of species, such as orders, sub-orders, families, sub-families,
and genera, they seem to be, at least at present, almost arbitrary.
Several of the best botanists, such as Mr. Bentham and others,
have strongly insisted on their arbitrary value. Instances could
be given amongst plants and insects, of a group first ranked by
practised naturalists as only a genus, and then raised to the rank of
a sub-family or family ; and this has been done, not because further
research has detected important structural differences, at first over-
looked, but because numerous allied species with slightly different
grades of difference, have been subsequently discovered.

All the foregoing rules and aids and difficulties in classification
may be explained, if I do not greatly deceive myself, on the view that
the Natural System is founded on descent with modification ; — that
the characters which naturalists consider as showing true affinity
between any two or more species, are those which have been in-
herited from a common parent, all true classification being genea-
logical;— that community of descent is the hidden bond which
naturalists have been unconsciously seeking, and not some unknown
plan of creation, or the enunciation of general propositions, and the
mere putting together and separating objects more or less alike.

But I must explain my meaning more fully. I believe that the
arrangement of the groups within each class, in due subordination
and relation to each other, must be strictly genealogical in order
to be natural; but that the amount of difference in the several
branches or groups, though allied in the same degree in blood to
their common progenitor, may differ greatly, being due to the
different degrees of modification which they have undergone ; and
this is expressed by the forms being ranked under different genera,
families, sections, or orders. The reader will best understand what
is meant, if he will take the trouble to refer to the diagram in the
fourth chapter. "We will suppose the letters A to L to represent

2 B

370 CLASSIFICATION. TChap. XIV.

allied genera existing during the Silurian epoch, and descended from
some still earlier form. In three of these genera (A, F, anvi I), a
species has transmitted modified descendants to the present day^
represented by the fifteen genera (a" to 2^^) on the uppermost
horizontal line. Now all these modified descendants from a single
species, are related in blood or descent in the same degree ; they
may metaphorically be called cousins to the same millionth degree ;
yet they differ widely and in different degrees from each other. The
forms descended from A, now broken up into two or three families,
constitute a distinct order from those descended from I, also broken
up into two families. Nor can the existing species, descended from
A, be ranked in the same genus with the parent A ; or those
from I, with the parent I. But the existing genus f^^ may be sup-
posed to have been but slightly modified ; and it will then rank with
the parent-genus F ; just as some few still living organisms belong
to Silurian genera. So that the comparative value of the differences
between these organic beings, which are all related to each other in
the same degree in blood, has come to be widely different. Never-
theless their genealogical arrangement remains strictly true, not
only at the present time, but at each successive period of descent.
All the modified descendants from A will have inherited something
in common from their common parent, as will all the descendants
from I ; so will it be with each subordinate branch of descendants,
at each successive stage. If, however, we suppose any descendant of
A, or of I, to have become so much modified as to have lost all traces
of its parentage, in this case, its place in the natural system will be
lost, as seems to have occurred with some few existing organisms.
All the descendants of the genus F, along its whole line of descent,
are supposed to have been but little modified, and they form a single
genus. But this genus, though much isolated, will still occupy its
proper intermediate position. The representation of the groups,
as here given in the diagram on a flat surface, is much too simple.
The branches ought to have diverged in all directions. If the
names of the groups had been simply written down in a linear
series, the representation would have been still less natural ; and it
is notoriously not possible to represent in a series, on a flat surface,
the affinities which we discover in nature amongst the beings of the
same group. Thus, the natural system is genealogical in its
arrangement, like a pedigree : but the amount of modification which
the different groups have undergone has to be expressed by ranking
them under different so-called genera, sub-families, families, sections,
orders, and classes.
It may be worth while to illustrate this view of classification, by

Ceaj XIV.] CLASSIFICATION. 371

taking the case of languages. If we possessed a perfect pedigree cf
mankind, a genealogical arrangement of the races of man would
afford the best classification of the various languages now spoken
throughout the world ; and if all extinct languages, and all inter-
mediate and slowly changing dialects, were to be included, such an
arrangement would be the only possible one. Yet it might be that
some ancient languages had altered very little and had given rise
to few new languages, whilst others had altered much owing to the
spreading, isolation, and state of civilisation of the several co-
descended races, and had thus given rise to many new dialects and
languages. The various degrees of difference between the languages
of the same stock, would have to be expressed by groups subordinate
to groups ; but the proper or even the only possible arrangement
would still be genealogical ; and this would be strictly natural, as
it would connect together all languages, extinct and recent, by the
closest affinities, and would give the filiation and origin of each
tongue.

In confirmation of this view, let us glance at the classification of
varieties, which are known or believed to be descended from a single
species. These are grouped under the species, with the sub-varieties
under the varieties ; and in some cases, as with the domestic
pigeon, with several other grades of difi"erence. Nearly the same
rules are followed as in classifying species. Authors have insisted
on the necessity of arranging varieties on a natural instead of an
artificial system; we are cautioned, for instance, not to class two
varieties of the pine-apple together, merely because their fruit,
though the most important part, happens to be nearly identical ;
no one puts the Swedish and common turnip together, though the
esculent and thickened stems are so similar. Whatever part is
found to be most constant, is used in classing varieties : thus the
great agriculturist Marshall says the horns are very useful for this
purpose with cattle, because they are less variable than the shape
or colour of the body, &c. ; whereas with sheep the horns are much
less serviceable, because less constant. In classing varieties, I ap-
prehend that if we had a real pedigree, a genealogical classification
would be universally preferred ; and it has been attempted in some
cases. For we might feel sure, whether there had been more or
less modification, that the principle of inheritance would keep the
forms together which were allied in the greatest number of points.
In tumbler pigeons, though some of the sub-varieties difier in the
important character of the length of the beak, yet all are kept
together from having the common habit of tumbling; but the
short-faced breed has nearly or quite lost this habit : neverthelesSj

2 B 2

372 CLASSIFICATION. [Chap. XIV,

without any thought on the subject, these tumhlers are kept in
the same group, because allied in blood and alike in some other
respects.

Viih species in a state of nature, every naturalist has in fact
brought descent into his classification ; for he includes in his
lowest grade, that of species, the two sexes ; and how enormously
these sometimes differ in the most important characters, is known
to every naturalist : scarcely a single fact can be predicated in
common of the adult males and hermaphrodites of certain cirri-
pedes, and yet no one dreams of separating them. As soon as the
three Orchidean forms, Monachanthus, Myanthus, and Catasetum,
which had previously been ranked as three distinct genera, were
known to be sometimes produced on the same plant, they were
immediately considered as varieties ; and now I have been able to
show that they are the male, female, and hermaphrodite forms
of the same species. The naturalist includes as one species the
various larval stages of the same individual, however much they
may differ from each other and from the adult, as well as the so-
called alternate generations of Steenstrup, which can only in a
technical sense be considered as the same individual. He includes
monsters and varieties, not from their partial resemblance to the
parent-form, but because they are descended from it.

As descent has universally been used in classing together the
individuals of the same species, though the males and females
and larvas are sometimes extremely different ; and as it has been
used in classing varieties which have undergone a certain, and
sometimes a considerable amount of modification, may not this
same element of descent have been unconsciously used in grouping
si)ecies under genera, and genera under higher groups, all under
the so-called natural system ? I believe it has been unconsciously
used ; and thus only can I understand the several rules and guides
which have been followed by our best system atists. As we have
no written pedigrees, we are forced to trace community of descent
by resemblances of any kind. Therefore we choose those characters
which are the least likely to have been modified, in relation to the
conditions of life to which each species has been recently exposed.
Eudimentary structures on this view are as good as, or even some-
times better than, other parts of the organisation. We care not how
trifling a character may be — let it be the mere inflection of the
angle of the jaw, the manner in which an insect's wing is folded,
whether the skin be covered by hair or feathers — if it prevail
throughout many and different species, especially those having very
different habits o-f life, it assumes high value ; for we can account

Chap. XIV.] ANALOGICAL RESEMBLANCES. 373

for its presence in so many forms with such different habits, only
by inheritance from a commoD parent. We may err in this respect
in regard to single points of structure, but when several characters,
let them be ever so trifling, concur throughout a large gi'oup of
beings having different habits, we may feel almost sure, on the
theory of descent, that these characters have been inherited from
a common ancestor ; and we know that such aggregated characters
have especial value in classification.

We can understand why a species or a group of species may
depart from its allies, in several of its most important characteristics,
and yet be safely classed with them. This may be safely done, and
is often done, as long as a sufficient number of characters, let them
be ever so unimportant, betrays the hidden bond of community
of descent. Let two forms have not a single character in com-
mon, yet, if these extreme forms are connected together by a chain
of intermediate groups, we may at once infer their community of
descent, and we put them all into the same class. As we find
organs of high physiological importance — those which serve to
preserve life under the most diverse conditions of existence — are
generally the most constant, we attach especial value to them;
but if these same organs, in another group or section of a group,
are found to differ much, we at once value them less in our
classification. We shall presently see why embryological cha-
racters are of such high classificatory importance. Geographical
distribution may sometimes be brought usefully into play in
classing large genera, because all the species of the same genus,
inhabiting any distinct and isolated region, are in all probability
descended from the same parents.

Analogical Eeserablances. — We can understand, on the above
views, the very important distinction between real affinities
and analogical or adaptive resemblances. Lamarck first called
attention to this subject, and he has been ably followed by
Macleay and others. The resemblance in the shape of the body
and in the fin-like anterior limbs between dugongs and whales,
and between these two orders of mammals and fishes, are ana-
logical. So is the resemblance between a mouse and a shrew-mouse
(Sorex), which belong to difi'erent orders; and the still closer
resemblance, insisted on by Mr. Mivart, between the mouse and
a small marsupial animal (Antechinus) of Australia. These latter
resemblances may be accounted for, as it seems to me, by adapta-
tion for similarly active movements through thickets and herbage,
together with concealment from enemies.

Amongst insects there are innumerable similar instances ; thus

374 CLASSIFICATION. [Char XIV.

Linnaeus, misled by external appearances, actually classed an
homopterous insect as a moth. We see something of the same
kind even with om* domestic varieties, as in the strikingly similar
shape of the body in the improved breeds of the Chinese and
common pig, which are descended from distinct species; and in
the similarly thickened stems of the common and speciBcally
distinct Swedish turnip. The resemblance between the greyhound
and the racehorse is hardly more fanciful than the analogicFS
which have been drawn by some authors between widely different
animals.

On the view of characters being of real importance for classifi-
cation, only in so far as they reveal descent, we can clearly under-
stand why analogical or adaptive characters, although of the utmost
importance to the welfare of the being, are almost valueless to the
systematist. For animals, belonging to two most distinct lines of
descent, may have become adapted to similar conditions, and thus
have assumed a close external resemblance ; but such resemblances
will not reveal — will rather tend to conceal their blood-relation'
ship. We can thus also understand the apparent paradox, that
the very same characters are analogical when one group is com-
pared with another, but give true affinities when the members of
the same group are compared together: thus, the shape of the
body and fin-like limbs are only analogical when whales are com-
pared with fishes, being adaptations in both classes for swimming
through the water ; but between the several members of the
whale family, the shape of the body and the fin-like limbs ofi'er
characters exhibiting true affinity ; for as these parts are so
nearly similar throughout the whole family, we cannot doubt
that they have been inherited from a common ancestor. So it is
with fishes.

Numerous cases could be given of striking resemblances in quite
distinct beings between single parts or organs, which have been
adapted for the same functions. A good instance is afforded by
the close resemblance of the jaws of the dog and Tasmanian wolf
or Thylacinus, — animals which are widely sundered in the natural
system. But this resemblance is confined to general appearance,
as in the prominence of the canines, and in the cutting shape
of the molar teeth. For the teeth really differ much : thus the dog
has on each side of the upper jaw four pre-molars and only two
molars ; whilst the Thylacinus has three pre-molars and four molars.
The molars also differ much in the two animals in relative size
and structure. The adult dentition is preceded by a widely dif-
ferent milk dentition. Any one may of course deny that the teeth

Chaf. XIV 1 ANALOGICAL RESEMBLANCES. 376

in either case have been adapted for tearing flesh, through the
natural selection of successive variations ; but if this be admitted
in the one case, it is unintelligible to me that it should be denied
in the other. I am glad to find that so high an authority as
Professor Flower has come to this same conclusion.

The extraordinary cases given in a former chapter, of widely
different fishes possessing electric organs, — of widely different
insects possessing luminous organs, — and of orchids and asclepiads
having pollen-masses with viscid discs, come under this same head
of analogical resemblances. But these cases are so wonderful that
they were introduced as difficulties or objections to our theory.
In all such cases some fundamental difference in the growth or
development of the parts, and generally in their matured structure,
can be detected. The end gained is the same, but the means,
though appearing superficially to be the same, are essentially dif-
ferent. The principle formerly alluded to under the term of ana-
logical variation has probably in these cases often come into play ;
that is, the members of the same class, although only distantly
allied, have inherited so much in common in their constitution,
that they are apt to vary under similar exciting causes in a similar
manner ; and this would obviously aid in the acquirement through
natural selection of parts or organs, strikingly like each other, inde-
pendently of their direct inheritance from a common progenitor.

As species belonging to distinct classes have often been adapted
by successive slight modifications to live under nearly similar
circumstances, — to inhabit, for instance, the three elements of land,
air, and water, — we can perhaps understand how it is that a
numerical parallelism has sometimes been observed between the
sub-groups of distinct classes. A naturalist, struck with a paral-
lelism of this nature, by arbitrarily raising or sinking the value
of the groups in several classes (and all our experience shows that
their valuation is as yet arbitrary), could easily extend the paral-
lelism over a wide range ; and thus the septenary, quinary, quater-
nary and ternary classifications have probably arisen.

There is another and curious class of cases in which close externa^
resemblance does not depend on adaptation to similar habits of life,
but has been gained for the sake of protection. I allude to the
wonderful maimer in which certain butterflies imitate, as first
described by Mr. Bates, other and quite distinct species. This
excellent observer has shown that in some districts of S. America,
where, for instance, an Ithomia abounds in gaudy swarms, another
butterfly, namely, a Leptalis, is often found mingled in the same
flock ; and the latter so closely resembles the Ithomia in every

376 CLASSIFICATION. [Chap. XIV.

shade and stripe of colour and even in the shape of its wings, that
Mr. Bates, with his eyes sharpened by collecting during eleven
years, was, though always on his guard, continually deceived.
When the mockers and the mocked are caught and compared,
they are found to be very different in essential structure, and to
belong not only to distinct genera, but often to distinct families.
Had this mimicry occurred in only one or two instances, it might
have been passed over as a strange coincidence. But, if we proceed
from a district where one Leptalis imitates an Ithomia, another mock-
ing and mocked species belonging to the same two genera, equally
close in their resemblance, may be found. Altogether no less than
ten genera are enumerated, which include species that imitate
other butterflies. The mockers and mocked always inhabit the
same region; we never find an imitator living remote from the
form which it imitates. The mockers are almost invariably rare
insects ; the mocked in almost every case abound in swarms. In
the same district in which a species of Leptalis closely imitates
an Ithomia, there are sometimes other Lepidoptera mimicking the
same Ithomia : so that in the same place, species of three genera
of butterflies and even a moth are found all closely resembling
a butterfly belonging to a fourth genus. It deserves especial notice
that many of the mimicking forms of the Leptalis, as well as of the
mimicked forms, can be shown by a graduated series to be merely
varieties of the same species ; whilst others are undoubtedly distinct
species. But why, it may be asked, are certain forms treated as
the mimicked and others as the mimickers ? Mr. Bates satis-
factorily answers this question, by showing that the form which
is imitated keeps the usual dress of the group to which it belongs,
whilst the counterfeiters have changed their dress and do not
resemble their nearest allies.

"We are next led to inquire what reason can be assigned for
certain butterflies and moths so often assuming the dress of another
and quite distinct form ; why, to the perplexity of naturalists, has
nature condescended to the tricks of the stage ? Mr. Bates has,
no doubt, hit on the true explanation. The mocked forms, which
always abound in numbers, must habitually escape destruction to
a large extent, otherwise they could not exist in such swarms ;
and a large amount of evidence has now been collected, showing
that they are distasteful to birds and other insect-devouring animals.
The mocking forms, on the other hand, that inhabit the same
district, are comparatively rare, and belong to rare groups ; hence
they must sufi'er habitually from some danger, for otherwise, from
the number of eggs laid by all butterflies, they, would in three 02

Chap. XIV.] ANALOGICAL RESEMBLANCES. 377

four generations swarm over the wliole country. ISTow if a member
of one of these persecuted and rare groups were to assume a dress
so like that of a well-protected species that it continually deceived
the practised eyes of an entomologist, it would often deceive pre-
daceous birds and insects, and thus often escape destruction. Mr.
Bates may almost be said to have actually witnessed the process
by which the mimickers have come so closely to resemble the
mimicked ; for he found that some of the forms of Leptalis which
mimic so many other butterflies, varied in an extreme degree. In
one district several varieties occurred, and of these one alone
resembled to a certain extent, the common Ithomia of the same
district. In another district there were two or three varieties, one
of which was much commoner than the others, and this closely
mocked another form of Ithomia. From facts of this nature,
Mr. Bates concludes that the Leptalis first varies ; and when a
variety happens to resemble in some degree any common butterfly
inhabiting the same district, this variety, from its resemblance to
a flourishing and little-persecuted kind, has a better chance of
escaping destruction from predaceous birds and insects, and is
consequently oftener preserved ; — " the less perfect degrees of re-
semblance being generation after generation eliminated, and only
the others left to propagate their kind." So that here we have an
excellent illustration of natural selection.

Messrs, Wallace and Trimen have likewise described several
equally striking cases of imitation in the Lepidoptera of the Malay
Archipelago and Africa, and with some other insects. Mr. Wallace
has also detected one such case with birds, but we have none with
the larger quadrupeds. The much greater frequency of imitation
with insects than with other animals, is probably the consequence
of their small size ; insects cannot defend themselves, excepting
indeed the kinds furnished with a sting, and I have never heard of
an instance of such kinds mocking other insects, though they are
mocked ; insects cannot easily escape by flight from the larger ani-
mals which prey on them ; therefore, speaking metaphorically, they
are reduced, like most weak creatures, to trickery and dissimulation.

It should be observed that the process of imitation probably never
commenced between forms widely dissimilar in colour. But starting
with species already somewhat like each other, the closest resem-
blance, if beneficial, could readily be gained by the above means ;
and if the imitated form was subsequently, and gradually modified
through any agency, the imitating form would be led along the
same track, and thus be altered to almost any extent, so that it
might ultimately assume an appearance or colouring wholly unlike

378 CLASSIFICATION. [Chap. XIV.

that of the other members of the family to which it belonged.
There % however, some difficulty on this head, for it is necessary
to suppose in some cases that ancient members belonging to several
distinct groups, before they had diverged to their present extent,
accidentally resembled a member of another and protected group
in a sufficient degree to afford some slight protection ; this having
given the basis for the subsequent acquisition of the most perfect
resemblance.

— On the Nature of the Affinities connecting Organic Beings,— As
the modified descendants of dominant species, belonging to the
larger genera, tend to inherit the advantages which made the groups
to which they belong large and their parents dominant, they are
almost sure to spread widely, and to seize on more and more places
in the economy of nature. The larger and more dominant groups
within each class thus tend to go on increasing in size ; and they
consequently supplant many smaller and feebler groups. Thus we
can account for the fact that all organisms, recent and extinct, are
included under a few great orders, and under still fewer classes. As
showing how few the higher groups are in number, and how widely
they are spread throughout the world, the fact is striking that the
discovery of Australia has not added an insect belonging to a new
class ; and that in the vegetable kingdom, as I learn from Dr. Hooker,
it has added only two or three families of small size.

In the chapter on Geological Succession I attempted to show, on
the principle of each group having generally diverged much in
character during the long-continued process of modification, how it
is that the more ancient forms of life often present characters in
some degree intermediate between existing groups. As some few of
the old and intermediate forms have transmitted to the present day
descendants but little modified, these constitute our so-called
osculant or aberrant species. The more aberrant any form is, the
greater must be the number of connecting forms which have been
exterminated and utterly lost. And we have some evidence of
aberrant groups having suffered severely from extinction, for they
are almost always represented by extremely few species ; and such
species as do occur are generally very distinct from each other,
which again implies extinction. The genera Ornithorhynchus and
Lepidosiren, for example, would not have been less aberrant had
each been represented by a dozen species, instead of as at present
by a single one, or by two or three. We can, I think, account for
this fact only by looking at aberrant groups as forms which have
been conquered by more successful competitors, with a few members
still preserved under unusually favourable conditions.

Chap. XIV.] AFFINITIES CONNECTING ORGANIC BEINGS. 379

Mr. Waterhouse has remarked that, when a member belonging
to one grope of animals exhibits an affinity to a quite distinct
group, this afifinity in most cases is general and not special ; thus,
according to Mr. Waterhouse, of all Kodents, the bizcacha is most
nearly related to Marsupials ; but in the points in which it ap-
proaches this order, its relations are general, that is, not to any one
marsupial species more than to another. As these points of affinity
are believed to be real and not merely adaptive, they must be due
in accordance with our view to inheritance from a common progeni-
tor. Therefore we must suppose either that all Rodents, including
the bizcacha, branched off from some ancient Marsupial, which will
naturally have been more or less intermediate in character with
respect to all existing Marsupials ; or that both Rodents and Marsu-
pials branched off from a common progenitor, and that both groups
have since undergone much modification in divergent directions.
On either view we must suppose that the bizcacha has retained,
by inheritance, more of the characters of its ancient progenitor than
have other Rodents ; and therefore it will not be specially related
to any one existing Marsupial, but indirectly to all or nearly all
Marsupials, from having partially retained the character of their
common progenitor, or of some early member of the group. On the
other hand, of all Marsupials, as Mr. Waterhouse has remarked, the
Phascolomys resembles most nearly, not any one species, but the
general order of Rodents. In this case, however, it may be strongly
suspected that the resemblance is only analogical, owing to the
Phascolomys having become adapted to habits like those of a
Rodent. The elder De Candolle has made nearly similar observations
on the general nature of the affinities of distinct families of plants.

On the principle of the multiplication and gradual divergence in
character of the species descended from a common progenitor,
together with their retention by inheritance of some characters in
common, we can understand the excessively complex and radiating
affinities by which all the members of the same family or higher
group are connected together. For the common progenitor of a
whole family, now broken up by extinction into distinct groups and
sub-groups, will have transmitted some of its characters, modified
in various ways and degrees, to all the species ; and they will con-
sequently be related to each other by circuitous lines of affinity of
various lengths (as may be seen in the diagram so often referred to),
mounting up through many predecessors. As it is difficult to show
the blood-relationship between the numerous kindred of any ancient
and noble family even by the aid of a genealcgical tree, and almost
impossible to do so without this aid, we can understand the extra-

380 CLASSIFICATION. [Chap. XIV

ordinary difficulty wnlch naturalists have experienced in describing,
without the aid of a diagram, the various affinities which they
perceive between the many living and extinct members of the same
great natural class.

Extinction, as we have seen in the fourth chapter, has played an
important part in defining and widening the intervals between the
several groups in each class. We may thus account for the distinct-
ness of whole classes from each other — for instance, of birds from
,all other vertebrate animals — by the belief that many ancient forms
of life have been utterly lost, through which the early progenitors
of birds were formerly connected with the early progenitors of
the other and at that time less differentiated vertebrate classes.
There has been much less extinction of the forms of life which once
connected fishes with batrachians. There has been still less within
some whole classes, for instance the Crustacea, for here the most
wonderfully diverse forms are still linked together by a long and
only partially broken chain of affinities. Extinction has only
defined the groups : it has by no means made them ; for if every
form which has ever lived on this earth were suddenly to reappear,
though it would be quite impossible to give definitions by which
each group could be distinguished, still a natural classification, or at
least a natural arrangement, would be possible. "We shall see this
by turning to the diagram; the letters, A to L, may represent
eleven Silurian genera, some of which have produced large groups of
modified descendants, with every link in each branch and sub-
branch still alive; and the links not greater than those between
existing varieties. In this case it would be quite impossible to give
definitions by which the several members of the several groups
could be distinguished from their more immediate parents and
descendants. Yet the arrangement in the diagram would still hold
good and would be natural ; for, on the principle of inheritance, all
the forms descended, for instance, from A, would have something
in common. In a tree we can distinguish this or that branch,
though at the actual fork the two unite and blend together. We
could not, as I have said, define the several groups ; but we could
pick out types, or forms, representing most of the characters of each
group, whether large or small, and thus give a general idea of the
value of the differences between them. This is what we should be
driven to, if we were ever to succeed in collecting all the forms in
any one class which have lived throughout all time and spac(i.
Assuredly we shall never succeed in making so perfect a collec-
tion : nevertheless, in certain classes, we are tending towards this
end ; and Milne Edwards has lately insisted, in an able paper, on

Chap. XIV.] AFFINITIES CONNECTING ORGANIC BEINGS. 381

the high importance of looking to types, whether or not we can
separate and define the groups to which such types belong.

Finally, we have seen that natural selection, which follows from
the struggle for existence, and which almost inevitably leads to
extinction and divergence of character in the descendants from any
one parent-species, explains that great and universal feature in
the affinities of all organic beings, namely, their subordination
in group under group. We use the element of descent in
classing the individuals of both sexes and of all ages under one
species, although they may have but few characters in common ;
we use descent in classing acknowledged varieties, however different
they may be from their parents ; and I believe that this element of
descent is the hidden bond of connexion which naturalists have
sought under the term of the Natural System. On this idea of the
natural system being, in so far as it has been perfected, genealogical
in its arrangement, with the grades of difierence expressed by the
terms genera, families, orders, &c., we can understand the rules
which we are compelled to follow in our classification. We can
■understand why we value certain resemblances far more than
others ; why we use rudimentary and useless organs, or others of
trifling physiological importance ; why, in finding the relations
between one group and another, we summarily reject analogical or
adaptive characters, and yet use these same characters within the
limits of the same group. We can clearly see how it is that all
living and extinct forms can be grouped together within a few great
classes ; and how the several members of each class are connected
together by the most complex and radiating lines of affinities. We
shall never, probably, disentangle the inextricable web of the
affinities between the members of any one class ; but when we have
a distinct object in view, and do not look to some unknown plan oi
creation, we may hope to make sure but slow progress.

Professor Hackel in his * Generelle Morphologic ' and in other
works, has recently brought his great knowledge and abilities to bear
on what he calls phylogeny, or the lines of descent of all organic
beings. In drawing up the several series he trusts chiefly to
embryological characters, but receives aid from homologous and
rudimentary organs, as well as from the successive periods at which
the various forms of life are believed to have first appeared in oui
geological formations. He has thus boldly made a great beginningj
and shows us how classification will in the future be treated.

382 MORPHOLOGY. [Chap. XIV

Movphology.

"We liave seen that the members of the same class, independently
of their habits of life, resemble each other in the general plan of
their organisation. This resemblance is often expressed by the
term " unity of type ; " or by saying that the several parts and organs
in the different species of the class are homologous. The whole
subject is included under the general term of Morphology. This is
one of the most interesting departments of natural history, and may
almost be said to be its very soul. What can be more curious than
that the hand of a man, formed for grasping, that of a mole for
digging, the leg of the horse, the paddle of the porpoise, and the
wing of the bat, should all be constructed on the same pattern, and
should include similar bones, in the same relative positions ? How
curious it is, to give a subordinate though striking instance, that
the hind-feet of the kangaroo, which are so well fitted for bounding
over the open plains, — those of the climbing, leaf-eating koala,
equally well fitted for grasping the branches of trees, — those of the
ground-dwelling, insect or root eating, bandicoots, — and those of
some other AustraHan marsupials, — should all be constructed on the
same extraordinary type, namely with the bones of the second and
third digits extremely slender and enveloped within the same skin_,
so that they appear like a single toe furnished with two claws.
Notwithstanding this similarity of pattern, it is obvious that the
hind feet of these several animals are used for as widely different
purposes as it is possible to conceive. The case is rendered all the
more striking by the American opossums, which follow nearly
the same habits of life as some of their Australian relatives, having
feet constructed on the ordinary plan. Professor Flower, from
whom these statements are taken, remarks in conclusion ; " We
may call this conformity to type, without getting much nearer to
an explanation of the phenomenon ; " and he then adds " but is it
not powerfully suggestive of true relationship, of inheritance from a
common ancestor ? "

Geoffrey St. Hilaire has strongly insisted on the high importance
of relative position or connexion in homologous parts ; they may
differ to almost any extent in form and size, and yet remain con-
nected together in the same invariable order. We never find, for
instance, the bones of the arm and fore-arm, or of the thigh and
leg, transposed. Hence the same names can be given to the homo-
logous bones in widely different animals. We see the same great
law in the construction of the mouths of insects : what can be more
different than the immensely long spiral proboscis of a sphinx-moth,

Chap. XIV.] MORPHOLOGY. 383

the curious folded one of a bee or bug, and the great jaws of a
beetle? — yet all these organs, serving for such widely different
purposes, are formed by infinitely numerous modifications of an
upper lip, mandibles, and two pairs of maxillae. The same law
governs the construction of the mouths and limbs of crustaceans.
So it is with the flowers of plants.

Nothing can be more hopeless than to attempt to explain this
similarity of pattern in members of the same class, by utility or
by the doctrine of final causes. The hopelessness of the attempt
has been expressly admitted by Owen in his most interesting work
on the ' Nature of Limbs.' On the ordinary view of the inde-
pendent creation of each being, we can only say that so it is ; —
that it has pleased the Creator to construct all the animals and
plants in each great class on a uniform plan; but this is not a
scientific explanation.

The explanation is to a large extent simple on the theory of the
selection of successive slight modifications, — each modification being
profitable in some way to the modified form, but often affecting by
correlation other parts of the organisation. In changes of this
nature, there will be little or no tendency to alter the original
pattern, or to transpose the parts. The bones of a limb might be
shortened and flattened to any extent, becoming at the same time
enveloped in thick membrane, so as to serve as a fin ; or a webbed
hand might have all its bones, or certain bones, lengthened to any
extent, with the membrane connecting them increased, so as to
serve as a wing ; yet all these modifications would not tend to alter
the framework of the bones or the relative connexion of the parts.
If we suppose that an early progenitor — the archetype as it may
be called — of all mammals, birds, and reptiles, had its limbs con-
structed on the existing general pattern, for whatever purpose they
served, we can at once perceive the plain signification of the homo-
logous construction of the limbs throughout the class. So with
the mouths of insects, we have only to suppose that their common
progenitor had an upper lip, mandibles, and two pairs of maxillse,
these parts being perhaps very simple in form ; and then natural
selection will account for the infinite diversity in the structure and
functions of the mouths of insects. Nevertheless, it is conceivable
that the general pattern of an organ might become so much
obscured as to be finally lost, by the reduction and ultimately by
the complete abortion of certain parts, by the fusion of other parts,
and by the doubling or multiplication of others, — variations which
we know to be within the limits of possibility. In the paddles of
the gigantic extinct sea-lizards, and in the mouths of certain

384 MORPHOLOGY. [Chap. XIV.

suctorial crustaceans, the general pattern seems thus to have beconie
partially obscured.

There is another and equally curious branch of our subject,
namely, serial homologies, or the comparison of the different parts
or organs in the same individual, and not of the same parts or
organs in different members of the same class. Most physiolo-
gists believe that the bones of the skull are homologous — that
is, correspond in number and in relative connexion — with the
elemental parts of a certain number of vertebrae. The anterior
and posterior limbs in all the higher vertebrate classes are plainly
homologous. So it is with the wonderfully complex jaws and
legs of crustaceans. It is familiar to almost every one, that in
a flower the relative position of the sepals, petals, stamens, and
pistils, as well as their intimate structure, are intelligible on the
view that they consist of metamorphosed leaves, arranged in a
spire. In monstrous plants, we often get direct evidence of the
possibility of one organ being transformed into another ; and v/e
can actually see, during the early or embryonic stages of develop-
ment in flowers, as well as in crustaceans and many other animals,
that organs, which when mature become extremely different are at
first exactly alike.

How inexplicable are the cases of serial homologies on the
ordinary view of creation! Why should the brain be enclosed
in a box composed of such numerous and such extraordinarily
shaped pieces of bone, apparently representing vertebrse? As
Owen has remarked, the benefit derived from the yielding of the
separate pieces in the act of parturition by mammals, will by no
means explain the same construction in the skulls of birds and
reptiles. Why should similar bones have been created to form
the wing and the leg of a bat, used as they are for such totally
different purposes, namely flying and walking ? Why should one
crustacean, which has an extremely complex mouth formed of
many parts, consequently always have fewer legs ; or conversely,
those with manj'- legs have simpler mouths? Why should the
sepals, petals, stamens, and pistils, in each flower, though fitted
for such distinct purposes, be all constructed on the same pattern ?

On the theory of natural selection, we can, to a certain extent,
answer these questions. We need not here consider how tiie bodies
of some animals first became divided into a series of segments,
or how they became divided into right and left sides, with corre-
sponding organs, for such questions are almost beyond investiga-
tion. It is, however, probable that some serial structures are
the result of cells multiplying by division, entailing the mnlti-

Chap. XIV.] MORPHOLOGY. 385

plication of the parts developed from such cells. It must suffice for
our purpose to bear in mind that an indefinite repetition of the
same part or organ is the common characteristic, as Owen has
remarked, of all low or little specialised forms ; therefore the
unknown progenitor of the Vertebrata probably possessed many-
vertebrae ; the unknown progenitor of the Articulata, many seg-
ments; and the unknown progenitor of flowering plants, many
Laves arranged in one or more spires. We have also formerly
S3en that parts many times repeated are eminently liable to vary,
not only in number, but in form. Consequently such parts,
being already present in considerable numbers, and being highly
variable, would naturally afford the materials for adaptation to the
most different purposes ; yet they would generally retain, through
the force of inheritance, plain traces of their original or fundamental
resemblance. They would retain this resemblance all the more,
as the variations, whicli afforded the basis for their subsequent
modification through natural selection, would tend from the first
to be similar ; the parts being at an early stage of growth alike,
and being subjected to nearly the same conditions. Such parts,
whether more or less modified, unless their common origin became
wholly obscured, would be serially homologous.

In the great class of molluscs, though the parts in distinct
species can be shown to be homologous, only a few serial homo-
logies, such as the valves of Chitons, can be indicated ; that is,
we are seldom enabled to say that one part is homologous with
another part in the same individual. And we can understand this
fact ; for in molluscs, even in the lowest members of the class, we
do not- find nearly so much indefinite repetition of any one part
as we find in the other great classes of the animal and vegetable
kingdoms.

But morphology is a much more complex subject than it at first
appears, as has lately been well shown in a remarkable paper by
Mr. E. Kay Lankester, who has drawm an important distinction
between certain classes of cases which have all been equally ranked
by naturalists as homologous. He proposes to call the structures
which resemble each other in distinct animals, owing to their
descent from a common progenitor with subsequent modification,
homogenous ; and the resemblances which cannot thus be accounted
for, he proposes to call homoplastic. For instance, he believes that
the hearts of birds and mammals are as a whole homogenous, —
that is, have been derived from a common progenitor ; but that
the four cavities of the heart in the two classes are homoplastic, —
that is, have been independently developed. Mr. Lankester al?o

2 c

386 DEVELOPMENT AND EMBRYOLOGY. [Chap. XIV.

adduces the close resemblance of the parts on the right and left
sides of the body, and in the successive segments of the same indi-
vidual animal ; and here we have parts commonly called homo-
logous, which bear no relation to the descent of distinct species
from a common progenitor. Homoplastic structures are the same
with those which I have classed, though in a very imperfect
manner, as analogous modifications or resemblances. Their forma-
tion may be attributed in part to distinct organisms, or to distinct
parts of the same organism, having varied in an analogous manner ;
and in part to similar modifications, having been preserved for
the same general purpose or function, — of which many instances
have been given.

Naturalists frequently speak of the skull as formed of metamor-
phosed vertebrse; the jaws of crabs as metamorphosed legs; the
stamens and pistils in flowers as metamorphosed leaves; but it
would in most cases be more correct, as Professor Huxley has
remarked, to speak of both skull and vertebrae, jaws and legs, &c.,
as having been metamorphosed, not one from the other, as they
now exist, but from some common and simpler element. Most
naturalists, however, use such language only in a metaphorical
sense; they are far from meaning that during a long course of
descent, primordial organs of any kind — vertebrse in the one case
and legs in the other — have actually been converted into skulls or
jaws. Yet so strong is the appearance of this j^having occurred,
that naturalists can hardly avoid employing language having this
plain signification. According to the views here maintained, such
language may be used literally ; and the wonderful fact of the
jaws, for instance, of a crab retaining numerous characters, which
they probably would have retained through inheritance, if they
had really been metamorphosed from true though extremely simple
legs, is in part explained.

Development and Embryology.

This is one of the most important subjects in the whole round of
natural history. The metamorphoses of insects, with which every
one is familiar, are generally effected abruptly by a few stages ;
but the transformations are in reality numerous and gradual,
though concealed. A certain ephemerous insect (Chloeon) during
its development, moults, as shown by Sir J. Lubbock, above
twenty times, and each time undergoes a certain amount of
change ; and in this case we see the act of metamorphosis per-
formed in a primary and gradual manner. Many insects, and

Chap. XIV.] DEVELOPMENT AND EMBRYOLOGY. 387

especially certain crustaceans, show us what wonderful changes
of structure can be effected during development. Such changes,

however, reach their acme in the so-called alternate generations
of some of the lower animals. It is, for instance, an astonishing

fact that a delicate branching coralline, studded with polypi and
attached to a submarine rock, should produce, first by budding and
then by transverse division, a host of huge floating jelly-fishes ;
and that these should produce eggs, from which are hatched
swimming animalcules, which attach themselves to rocks and
become developed into branching corallines ; and so on in an
endless cycle. The belief in the essential identity of the process
of alternate generation and of ordinary metamorphosis has been
greatly strengthened by Wagner's discovery of the larva or maggot
of a fly, namely the Cecidomyia, producing asexually other larvse,
and these others, which finally are developed into mature males and
females, propagating their kind in the ordinary manner by eggs.

It may be worth notice that when Wagner's remarkable discovery
was first announced, I was asked how was it possible to account
for the larvse of this fly having acquired the power of asexual
reproduction. As long as the case remained unique no answer
could be given. But already Grimm has shown that another fly,
a Chironomus, reproduces itself in nearly the same manner, and he
believes that this occurs frequently in the Order. It is the pupa,
and not the larva, of the Chironomus which has this power ; and
Grimm further shows that this case, to a certain extent, " unites
that of the Cecidomyia with the parthenogenesis of the Coccidae ;" —
the term parthenogenesis implying that the mature females of the
Coccidai are capable of producing fertile eggs without the con-
course of the male. Certain animals belonging to several classes
are now known to have the power of ordinary reproduction at an
imusually early age ; and we have only to accelerate partheno-
genetic reproduction by gradual steps to an earlier and earlier age,
— Chironomus showing us an almost exactly intermediate stage,
viz., that of the pupa — and we can perhaps account for the mar-
vellous case of the Cecidomyia.

It has already been stated that various parts in the same indi-
vidual which are exactly alike during an early embryonic period,
become widely different and serve for widely different purposes in
the adult state. So again it has been shown that generally the
embryos of the most distinct species belonging to the same class
are closely similar, but become, when fully developed, widely dis-
similar. A better proof of this latter fact cannot be given than
the statement by Von Baer that " the embryos of mammalia, of.

2 c 2

388 DEVELOPMENT AND EMBRYOLOGY. [Chap. XIV.

*' birds, lizards, and snakes, probably also of cbelonia, are in their
" earliest states exceedingly like one another, both as a whole and
*' in the mode of development of their parts ; so much so, in fact,
" that we can often distinguish the embryos only by their size.
" In my possession are two little embryos in spirit, whose names
" I have omitted to attach, and at present I am quite unable to say
" to what class they belong. They may be lizards or small birds,
" or very young mammalia, so complete is the similarity in the
" mode of formation of the head and trunk in these animals. The
" extremities, however, are still absent in these embryos. But
" even if they had existed in the earliest stage of their develop-
" ment we should learn nothing, for the feet of lizards and mam-
" mals, the wings and feet of birds, no less than the hands and feet
*' of man, all arise from the same fundamental form." The larvae
of most crustaceans, at corresponding stages of development, closely
resemble each other, however different the adults may become j
and so it is with very many other animals. A trace of the law
of embryonic resemblance occasionally lasts till a rather late age :
thus birds of the same genus, and of allied genera, often resemble
each other in their immature plum.age ; as we see in the spotted
feathers in the young of the thrush group. In the cat tribe, most
of the species when adult are striped or spotted in lines; and
stripes or spots can be plainly distinguished in the whelp of the
lion and the puma. We occasionally though rarely see something
of the same kind in plants ; thus the first leaves of the ulex or
furze, and the first leaves of the phyllodineous acacias, are pinnate
or divided like the ordinary leaves of the leguminosse.

The points of structure, in which the embryos of widely different
animals within the same class resemble each other, often have no
direct relation to their conditions of existence. We cannot, for
instance, suppose that in the embryos of the vertebrata the peculiar
loop-like courses of the arteries near the branchial slits are related
to similar conditions, — in the young mammal which is nourished in
the womb of its mother, in the egg of the bird which is hatched
in a nest, and in the spawn of a frog under water. We have no
more reason to believe in such a relation, than we have to believe
that the similar bones in the hand of a man, wing of a bat, and fin
of a porpoise, are related to similar conditions of life. No one
supposes that the stripes on the whelp of a lion, or the spots on
the young blackbird, are of any use to these animals.

The case, however, is different when an animal during any part
of its embryonic career is active, and has to provide for itself. The
period of activity may come on earlier or later in life j but whenever

Chap. XIV.] DEVELOPMENT AND EMBRYOLOGY. 389

it comes on, the adaptation of the larva to its conditions of life is
just as perfect and as beautiful as in the adult animal. In how
important a manner this has acted, has recently been well shown
by Sir J. Lubbock in his remarks on the close similarity of the
larvae of some insects belonging to very different orders, and on
the dissimilarity of the larvae of other insects within the same
order, according to their habits of life. Owing to such adaptations,
the similarity of the larvae of allied animals is sometimes greatly
obscured ; especially when there is a division of labour during the
different stages of development, as when the same larva has during
one stage to search for food, and during another stage has to search
for a place of attachment. Cases can even be given of the larvse of
allied species, or groups of species, differing more from each other
than do the adults. In most cases, however, the larvas, though
active, still obey, more or less closely, the law of common embryonic
resemblance. Cirripedes afford a good instance of this ; even the
illustrious Cuvier did not perceive that a barnacle was a crustacean :
but a glance at the larva shows this in an unmistakable manner.
So again the two main divisions of cirripedes, the pedunculated and
sessile, though differing widely in external appearance, have larvaa
in all their stages barely distinguishable.

The embryo in the course of development generally rises in
organisation ; I use this expression, though I am aware that it is
hardly possible to define clearly what is meant by the organisation
being higher or lower. But no one probably will dispute that the •
butterfly is higher than the caterpillar. In some cases, however,
the mature animal must be considered as lower in the scale than
the larva, as with certain parasitic crustaceans. To refer once
again to cirripedes : the larvse in the first stage have three pairs of
locomotive organs, a simple single eye, and a probosciformed mouth,
with which they feed largely, for they increase much in size. In
the second stage, answering to the chrysalis stage of butterflies,
they have six pairs of beautifully constructed natatory legs, a pair
of magnificent compound eyes, and extremely complex antennae ;
but they have a closed and imperfect mouth, and cannot feed:
their function at this stage is, to search out by their well-developed
organs of sense, and to reach by their active powers of swimming,
a proper place on which to become attached and to undergo their
final metamorphosis. "When this is completed they are fixed for
life : their legs are now converted into prehensile organs ; they
again obtain a well-constructed mouth ; but they have no antennae,
and their two eyes are now reconverted into a minute, single
simple eye-spot. In this last and complete state, cirripedes may

S'&O DEVELOPMENT AND EMBRYOLOGY. [Chap. XIV

be considered as either more highly or more lowly organised than
they were in the larval condition. But in some genera the larv©
become developed into hermaphrodites having the ordinary strac-
ture, and into what I have called complemental males ; and in the
latter the development has assm-edly been retrograde, for the male
is a mere sack, which lives for a short time and is destitute of
mouth, stomach, and every other organ of importance, excepting
those for reproduction.

We are so much accustomed to see a difiterence in structure be-
tween the embryo and the adult, that we are tempted to look at
this difference as in some necessary manner contingent on growth.
But there is no reason why, for instance, the wing of a bat, or the^
fin of a porpoise, should not have been sketched out with all their
parts in proper proportion, as soon as any part became visible. In
some whole groups of animals and in certain members of other
groups this is the case, and the embryo does not at any period differ
widely from the adult : thus Owen has remarked in regard to cuttle-
fish, " there is no metamorphosis ; the cephalopodic character is
manifested long before the parts of the embryo are completed."
Land-shells and fresh-water crustaceans are born having their proper
forms, whilst the marine m^embers of the same two great classes pasa
through considerable and often great changes during their develop-
ment. Spiders, again, barely undergo any metamorphosis. The
larv£e of most insects pass through a worm-like stage, whether they
are active and adapted to diversified habits, or are inactive from
being placed in the midst of proper nutriment or from being fed by
their parents ; but in some few cases, as in that of Aphis, if we look
to the admirable drawings of the development of this insect, by
Professor Huxley, we see hardly any trace of the vermiform stage.

Sometimes it is only the earlier developmental stages which fail.
Thus Fritz Miiller has made the remarkable discovery that certain
shrimp-like crustaceans (allied to Penoeus) first appear under the
simple nauplius-form, and after passing through two or more zoea-
stages, and then through the mysis-stage, finally acquire their
mature structure : now in the whole great malacostracan order, to
which these crustaceans belong, no other member is as yet known
to be first developed under the nauplius-form, though many appear
as zoeas ; nevertheless Miiller assigns reasons for his belief, that if
there had been no suppression of development, all these crustaceans
would have appeared as nauplii.

How, then, can we explain these several facts in embryology, —
namely, the very general, though not universal, difference in struc-
ture between the embryo and the adult ^ — the various parts in the'

Chap, XIV.] DEVELOPMENT AND EMBRYOLOGY. 391

same individual embryo, which ultimately become very unlike and
serve for diverse purposes, being at an early period of growth alike ;
■ — the common, but not invariable, resemblance between the em-
bryos or larva3 of the most distinct species in the same class ; —
the embrj'-o often retaining whilst within the egg or womb, struo
tures which are of no service to it, either at that or at a later
period of life ; on the other hand larvse, which have to provide for
their own wants, being perfectly adapted to the surrounding condi-
tions ; — and lastly the fact of certain larva? standing higher in the
scale of organisation than the mature animal into which they are de-
veloped ? I believe that all these facts can be explained, as follows.

It is commonly assumed, perhaps from monstrosities affecting the
embryo at a very early period, that slight variations or individual
differences necessarily appear at an equally early period. We have
little evidence on this head, but what we have certainly points the
other way ; for it is notorious that breeders of cattle, horses, and
various fancy animals, cannot positively tell, until some time after
birth, what will be the merits or demerits of their young animals.
We see this plainly in our own children ; we cannot tell whether a
child will be tall or short, or what its precise features will be. The
question is not, at what period of life each variation may have been
caused, but at what period the effects are displayed. The cause
may have acted, and I believe often has acted, on one or both
parents before the act of generation. It deserves notice that it is
of no importance to a very young animal, as long as it remains in
its miother's womb or in the egg, or as long as it is nourished and
protected by its parent, whether most of its characters are acquired
a little earlier or later in life. It would not signify, for instance,
to a bird which obtained its food by having a much-curved beak
whether or not whilst young it possessed a beak of this shape, as
long as it was fed by its parents.

I have stated in the first chapter, that at whatever age a variation
first appears in the parent, it tends to re-appear at a corresponding
age in the offspring. Certain variations can only appear at corres-
ponding ages ; for instance, peculiarities in the caterpillar, cocoon,
or imago states of the silk-moth : or, again, in the full-grown horns
of cattle. But variations, which, for all that we can see might
have first appeared either earlier or later in life, likewise tend to re-
appear at a corresponding age in the offspring and parent. I am
far from meaning that this is invariably the case, and I could give
several exceptional cases of variations (taking the word in the
largest sense) which have supervened at an earlier age m the chilb
than in the parent.

392 DEVELOPMENT AND EMBRYOLOGY. [Chap. X17,

These two principles, namely, that slight variations generally
appear at a not very early period of life, and are inherited at a cor-
responding not early period, explain, as I believe, all the above
specified leading facts in embryology. But first let lis look to a few
analogous cases in our domestic varieties. Some authors who have
written on Dogs, maintain that the greyhound and bulldog, though
so dififerent, are really closely allied varieties, descended from the
same wild stock ; hence I was curious to see how far their puppies
differed from each other : I was told by breeders that they differed
just as much as their parents, and this, judging by the eye, seemed
almost to be the case ; but on actually measuring the old dogs
and their six-days-old puppies, I found that the puppies had not
acquired nearly their full amount of proportional difference. So,
again, I was told that the foals of cart and race-horses — breeds
which have been almost wholly formed by selection under domesti-
cation— differed as much as the full-grown animals ; but having had
careful measurements made of the dams and of three-days-old
colts of race and heavy cart-horses, I find that this is by no means
the case.

As we have conclusive evidence that the breeds of the Pigeon
are descended from a single wild species, I compared the young
within twelve hours after being hatched ; I carefully measured the
proportions (but will not here give the details) of the beak, width
of mouth, length of nostril and of eyelid, size of feet and length of
leg, in the wild parent-species, in pouters, fantails, runts, barbs,
dragons, carriers, and tumblers. Kow some of these birds, when,
mature, differ in so extraordinary a manner in the length and form
of beak, and in other characters, that they would certainly have
been ranked as distinct genera if found in a state of nature. But
when the nestling birds of these several breeds were placed in a row,
though most of them could just be distinguished, the proportional
differences in the above specified points were incomparably less than
in the full-grown birds. Some characteristic points of difference —
for instance, that of the width of mouth — could hardly be detected
in the young. But there was one remarkable exception to this rule,
for the young of the short-faced tumbler differed from the young of
the wild rock-pigeon and of the other breeds, in almost exactly the
same proportions as in the adult state.

These facts are explained by the above two principles. Fanciers
select their dogs, horses, pigeons, &c., for breeding, when nearly
grown up : they are indifferent whether the desired qualities are
acquired earlier or later in life, if the full-grown animal possesses
them. And the cases just given, more especially that of the

Chap. XIV.] DEVELOPMENT AND EMBRYOLOGY. 393

pigeons, show that the characteristic differences which have "been
accumulated by man's selection, and which give value to his breeds,
<\o not generally appear at a very early period of life, and are inhe-
rited at a corresponding not early period. But the case of the short-
faced tumbler, which when twelve hours old possessed its proper
characters, proves that this is not the universal rule ; for here the
characteristic differences must either have appeared at an earlier
period than usual, or, if not so, the differences must have been in-
hei'ited, not at a corresponding, but at an earlier age.

Now let us apply these two principles to species in a state ot
nature. Let us take a group of birds, descended from some ancient
form and modified through natural selection for different habits.
Then, from the many slight successive variations having supervened
in the several species at a not early age, and having been inherited
at a corresponding age, the young will have been but little modi-
fied, and they will still resemble each other much more closely
than do the adults, — ^just as we have seen with the breeds of the
pigeon. We may extend this view to widely distinct structures and
to whole classes. The fore-limbs, for instance, which once served
as legs to a remote progenitor, may have become, through a long
course of modification, adapted in one descendant to act as hands,
in another as paddles, in another as wings ; but on the above
two principles the fore-limbs will not have been much modified
in the embryos of these several forms ; although in each form
the fore-limb will differ greatly in the adult state. Whatever
influence long-continued use or disuse may have had in modifying
the limbs or other parts of any species, this will chiefly or solely
have affected it when nearly mature, when it was compelled ta
use its full powers to gain its own living ; and the effects thus
produced will have been transmitted to the offspring at a cor-
responding nearly mature age. Thus the young will not be modi-
fied, or will be modified only in a slight degree, through the effects
of the increased use or disuse of parts.

With some animals the successive variations may have supervened
at a very early period of life, or the steps may have been inherited
at an earlier age than that at which they first occurred. In either
of these cases, the young or embryo will closely resemble the
mature parent-form, as we have seen with the short-faced tumbler.
And this is the rule of development in certain whole groups, or
in certain sub-groups alone, as with cuttle-fish, land-shells, fresh-
water crustaceans, spiders, and some members of the great class of
insects. With respect to the final cause of the young in such
groups not passing through any metamorphosis, we can see that this

State Historical ana
NatucaJ History Socie:\

394 DEVELOPMENT AND EMBRrOLOGY. [Chap. XIV.

would follow from the following contingences ; namely, from the
young having to provide at a very early age for their own wants,
and from their following the same habits of life with their parents ;,
for in this case, it would be indispensable for their existence that
they should ' be modified in the same manner as their parents.
Again, with respect to the singular fact that many terrestrial and
fresh-water animals do not undergo any metamorphosis, whilst
marine members of the same groups pass through various transfor-
mations, Fritz Miiller has suggested that the process of slowly
modifying and adapting an animal to live on the land or in fresh
water, instead of in the sea, would be greatly simplified by its not
passing through any larval stage ; for it is not probable that places
well adapted for both the larval and mature stages, under such new
and greatly changed habits of life, would commonly be found un-
occupied or ill-occupied by other organisms. In this case the
gradual acquirement at an earlier and earlier age of the adult
structure would be favoured by natural selection ; and all traces of
former metamorphoses would finally be lost.

If, on the other hand, it profited the young of an animal to follow
habits of life slightly different from those of the parent-form, and
consequently to be constructed on a slightly different plan, or if
it profited a larva already different from its parent to change still
further, then, on the principle of inheritance at corresponding ages,
the young or the larva3 might be rendered by natural selection more
and more different from their parents to any conceivable extent.
Differences in the larva might, also, become correlated with succes-
sive stages of its development; so that the larva, in the first stage,
might come to differ greatly from the larva in the second stage, as
is the case with many animals. The adult might also become fitted
for sites or habits, in which organs of locomotion or of the senses,
&c., would be useless ; and in this case the metamorphosis would be
retrograde.

From the remarks just made we can see how by changes of struc-
ture in the young, in conformity with changed habits of life, to-
gether with inheritance at corresponding ages, animals might come
to pass through stages of development, perfectly distinct from the
primordial condition of their adult progenitors. Most of our best
authorities are now convinced that the various larval and pupal
stages of insects have thus been acquired through adaptation, and.
not through inheritance from some ancient form. The curious case
of Sitaris — a beetle which passes through certain unusual stages ol
development — will illustrate how this might occur. The first larval
from is described by M. Fabre, as an active, minute insect, fumiahed

Chap. XIV.] DEVELOPMENT AND EMBRYOLOGY. 395

with six legs, two long antenna?, and four eyes. These larvae aro
hatched in the nests of bees ; and when the male-bees emerge from
their burrows, in the spring, which they do before the females, the
larvae spring on them, and afterwards crawl on to the females whilst
paired with the males. As soon as the female bee deposits her
eggs on the surface of the honey stored in the cells, the larvjB of
the Sitaris leap on the eggs and devour them. Afterwards they
undergo a complete change ; their eyes disappear ; their legs and
antennse become rudimentary, and they feed on honey ; so that they
now more closely resemble the ordinary laiT£e of insects ; ultimately
they undergo a further transformation, and finally emerge as the
perfect beetle. Now, if an insect, undergoing transformations like
those of the Sitaris, were to become the progenitor of a whole new
class of insects, the course of development of the new class would
be widely different from that of our existing insects ; and the first
larval stage certainly would not represent the former condition of
any adult and ancient form.

On the other hand it is highly probable that with many animals
the embryonic or larval stages show us, more or less completely, the
condition of the progenitor of the whole group in its adult state.
In the great class of the Crustacea, forms wonderfully distinct from
each other, namely, suctorial parasites, cirripedes, entomostraca, and
even the malacostraca, appear at first as larv-aB under the naupiius-
form ; and as these larva3 live and feed in the open sea, and are not
adapted for any peculiar habits of life, and from other reasons
assigned by Fritz MUller, it is probable that at some very remote
period an independent adult animal, resembling the Nauplius,
existed, and subsequently produced, along several divergent lines of
descent, the above-named great Crustacean groups. So again it is
probable, from what we know of the embryos of mammals, birds,
fishes, and reptiles, that these animals are the modified descendants
of some ancient progenitor, which was furnished in its adult state
with branchiEe, a swim-bladder, four fin-like limbs, and a long tail,
all fitted for an aquatic life.

As all the organic beings, extinct and recent, which have ever
lived, can be arranged within a few great classes ; and as all within
each class have, according to our theory, been connected together
by fine gradations, the best, and, if our collections were nearly per-
fect, the only possible arrangement, would be genealogical ; descent
being the hidden bond of connexion which naturalists have been
seeking under the term of the Natural System. On this view we
am understand how it is that, in the eyes of most naturalists, the
Btructurtf of the embryo is even more important for classification

396 DEVELOPMENT AND EMBRYOLOGY. [Chap. XIV.

than that of the adult. In two or more groups of animals, liowever
much they may differ from each other in structure and habits in
their adult condition, if the}'- pass through closely similar embryonic
stages, we may feel assured that they all are descended from one
parent-form, and are therefore closely related. Thus, community
in embryonic structure reveals community of descent ; but dissi-
milarity in embryonic development does not prove discommunity of
descent, for in one of two groups the developmental stages may
have been suppressed, or may have been so greatly modified through
adaptation to new habits of life, as to be no longer recognisable.
Even in groups, in which the adults have been modified to an ex-
treme degree, community of origin is often revealed by the structure
of the larvse ; we have seen, for instance, that cirripedes, though
externally so like shell-fish, are at once known by their larva? to
belong to the great class of crustaceans. As the embryo often
shows us more or less plainly the structure of the less modified and
ancient progenitor of the group, we can see why ancient and extinct
forms so often resemble in their adult state the embryos of existing
species of the same class. Agassiz believes this to be a universal
law of nature ; and we may hope hereafter to see the law proved true.
It can, however, be proved true only in those cases in which the
ancient state of the progenitor of the group has not been wholly
obliterated, either by successive variations having supervened at a
very early period of growth, or by such variations having been inhe-
rited at an earlier age than that at which they first appeared. It
should also be borne in mind, that the law may be true, but yet,
owing to the geological record not extending far enough back in
time, may remain for a long period, or for ever, incapable of demon-
stration. The law will not strictly hold good in those cases in
which an ancient form became adapted in its larval state to some
special line of life, and transmitted the same larval state to a whole
group of descendants; for such larv^ vjill not resemble any still
more Ancient form in its adult state.

Thus, as it seems to me, the leading facts in embryology, which
are second to none in importance, are explained on the principle of
variations in the many descendants from some one ancient proge-
nitor, having appeared at a not very early period of life, and having
been inherited at a corresponding period. Embryology rises greatly
in interest, when we look at the embryo as a picture, more or less
obscm*ed, of the progenitor, either in its adult or larval state^ of all
the members of the same sreat class.

Chap. XIV.] RUDIMENTARY ORGANS. 397

Rudimentary, AtropJded, and Aborted Organs.

Organs or parts in this strange condition, bearing the plain stamp
of inutility, are extremely common, or even general, throughout
nature. It would be impossible to name one of the higher animals
in which some part or other is not in a rudimentary condition. In
the mammalia, lor instance, the males possess rudimentary mammse ;
in snakes one lobe of the lungs is rudimentary; in birds the
" bastard- wing " may safely be considered as a rudimentary digit,
and in some species the whole wing is so far rudimentary that it
cannot be used for flight. What can be more curious than the
presence of teeth in foetal whales, which when grown up have not a
tooth in their heads ; or the teeth, which never cut through the
gums, in the upper jaws of unborn calves ?

liudimentary organs plainly declare their origin and meaning in
various ways. There are beetles belonging to closely allied species,
or even to the same identical species, which have either full-sized
and perfect wings, or mere rudiments of membrane, which not
rarely lie under wing-covers firmly soldered together; and in these
cases it is impossible to doubt, that the rudiments represent wings.
Rudimentary organs sometimes retain their potentiality : this oc-
casionally occurs with the mammse of male mammals, which have
been known to become well developed and to secrete milk. Sc
again in the udders in the genus Bos, there are normally four deve-
loped and two rudimentary teats ; but the latter in our domestic
cows sometimes become well developed and yield milk. In regard
to plants the petals are sometimes rudimentary, and sometimes well-
developed in the individuals of the same species. In certain plants
having separated sexes Kolreuter found that by crossing a species, in
which the male flowers included a rudiment of a pistil, with an
hermaphrodite species, having of course a well-developed pistil, the
rudiment in the hybrid offspring was much increased in size ; and
this clearly shows that the rudimentary and perfect pistils are es-
sentially alike in nature. An animal may possess various parts in
a perfect state, and yet they may in one sense be rudimentary, for
they are useless : thus the tadpole of the common Salamander oi
Water-newt, as Mr. G. H. Lewes remarks, " has gills, and passes
*' its existence in the water ; but the Salamandra atra, which lives
" high up among the mountains, brings forth its young full-formed.
" This animal never lives in the water. Yet if we open a gravid
" female, we find tadpoles inside her with exquisitely feathered
" gills ; and when placed in water they swim about like the tad-
** poleti of the water-newt. Obviously this aquatic organisation has

398 RUDIMENTARY, ATROPHIEI>, [Chap. XIV.

" no reference to the future life of the animal, nor has it any adap-
" tation to its embryonic condition ; it has solely reference to
" ancestral adaptations, it repeats a phase in the development of its
" progenitors."

An organ, serving for two purposes, may become rudimentary or
utterly aborted for one, even the more important purpose, and remain
perfectly efficient for the other. Thus in plants, the office of the
pistil is to allow the pollen-tubes to reach the ovules within the
ovarium. The pistil consists of a stigma supported on a style ; but
in some Compositse, the male florets, which of course cannot be
fecundated, have a rudimentary pistil, for it is not crowned with a
stigma ; but the style remains well developed and is clothed in the
usual manner with hairs, which serve to brush the pollen out of the
surrounding and conjoined anthers. Again, an organ may become
rudimentary for its proper purpose, and be used for a distinct
one: in certain fishes the swim-bladder seems to be rudimentary
for its proper function of giving buoyancy, but has become con-
verted into a nascent breathing organ or lung. Many similar in-
stances could be given.

Useful organs, however little they may be developed, unless wc
have reason to suppose that they were formerly more highly deve-
loped, ought not to be considered as rudimentary. They may be
in a nascent condition, and in progress towards further develop-
ment. Eudimentary organs, on the other hand, are either quite use-
less, such as teeth which never cut through the gums, or almost
useless, such, as the wings of an ostrich, which serve merely as
sails. As organs in this condition would formerlj'", when still less
developed, have been of even less use than at present, they cannot
formerly have been produced through variation and natural selection,
which acts solely by the preservation of useful modifications. They
have been partially retained by the power of inheritance, and re-
late to a former state of things. It is, however, often difficult to
distinguish between rudimentary and nascent organs ; for we can
judge only by analogy whether a part is capable of further deve-
lopment, in which case alone it deserves to be called nascent.
Organs in this condition will always be somewhat rare ; for beings
thus provided will commonly have been supplanted by their suc-
cessors with the same organ in a more perfect state, and conse-
quently will have become long ago extinct. The wing of the
penguin is of high service, acting as a fin; it may, therefore,
represent the nascent state of the wing : not that I believe this to
be the case ; it is more probably a reduced organ, modified for a new
function: the vnng of tbj Apteryx, on the other hand, is quite

Chap. XIV.] AND ABORTED ORGANS. 399

useless, and is truly rudimentary. Owen considers the simple fila-
mentary limbs of the Lepidosiren as the " beginnings of organs
which attain full functional development in higher vertebrates ; *"
but, according to the view lately advocated by Dr. GUnther, they
are probably remnants, consisting of the persistent axis of a fin,
with the lateral rays or branches aborted. The mammary glands of
the Ornithorhynchus may be considered, in comparison with the
udders of a cow, as in a nascent condition. The ovigercus frena of
certain cirripedes, which have ceased to give attachment to the
ova and are feebly developed, are nascent branchise.

Eudimentary organs in the individuals of the same species are
very liable to vary in the degree of their development and in other
respects. In closely allied species, also, the extent to which the
same organ has been reduced occasionally differs much. This latter
fact is well exemplified in the state of the wings of female moths
belonging to the same family. Rudimentary organs may be utterly
aborted ; and this implies, that in certain animals or plants, parts
are entirely absent which analogy would lead us to expect to find in
them, and which are occasionally found in monstrous individuals.
Thus in most of the Scrophulariacese the fifth stamen is utterly
aborted ; yet we may conclude that a fifth stamen once existed, for
a rudiment of it is found in many species of the family, and this
rudiment occasionally becomes perfectly developed, as may some-
times be seen in the common snap-dragon. In tracing the homo-
logies of any part in different members of the same class, nothing
is more common, or, in order fully to understand the relations of
the parts, more useful than the discovery of rudiments. This is well
shown in the drawings given by Owen of the leg-bones of the horse,
ox, and rhinoceros.

It is an important fact that rudimentary organs, such as teeth in
the upper jaws of whales and ruminants, can often be detected
in the embryo, but afterwards wholly disappear. It is also, I
believe, a universal rule, that a rudimentary part is of greater size
in the embryo relatively to the adjoining parts, than in the adult ;
so that the organ at this early age is less rudimentary, or even
cannot be said to be in any degree rudimentary. Hence rudimen-
tary organs in the adult are often said to have retained their
embryonic condition.

I have now given the leading facts with respect to rudimentary
organs. In reflecting on them, every one must be struck with
astonishment; for the same reasoning power which tells us that
most parts and organs are exquisitely adapted for certain purposes,
tells us with equal plainness that these rudimentary or atrophied

400 RUDIMENTARY, ATROPHIED, [Chap. XIV,

organs are imperfect and useless. In works on natural history,
rudimentary organs are generally said to have been created " for
the sake 3f symmetry," or in order " to complete the scheme of
nature." But this is not an explanation, merely a re-statement of
the fact. Nor is it consistent with itself: thus the boa-constrictor
has rudiments of hind-limbs and of a pelvis, and if it be said that
these bones have been retained " to complete the scheme of nature,"
why, as Professor Weismann asks, have they not been retained by
other snakes, which do not possess even a vestige of these same
bones ? What would be thought of an astronomer who maintained
that the satellites revolve in elliptic courses round their planets
" for the sake of symmetry,'' because the planets thus revolve
round the sun ? An eminent physiologist accounts for the presence
of rudimentary organs, by supposing that they serve to excrete
matter in excess, or matter injurious to the system ; but can we
suppose that the minute papilla, which often represents the pistil in
male flowers, and which is formed of mere cellular tissue, can thus
act ? Can we suppose that rudimentary teeth, which are subse-
quently absorbed, are beneficial to the rapidly growing embryonic
calf by removing matter so precious as phosphate of lime ? When
a man's fingers have been amputated, imperfect nails have been
known to appear on the stumps, and I could as soon believe that
these vestiges of nails are developed in order to excrete horny
matter, as that the rudimentary nails on the fin of the manatee
have been developed for this same purpose.

On the view of descent with modification, the origin of rudimen-
tary organs is comparatively simple ; and we can understand to a
large extent the laws governing their imperfect development. We
have plenty of cases of rudimentary organs in our domestic pro-
ductions,— as the stump of a tail in tailless breeds, — the vestige of
an ear in earless breeds of sheep, — the reappearance of minute
dangling horns in hornless breeds of cattle, more especially,
according to Youatt, in young animals, — and the state of the
whole flower in the cauliflower. We often see rudiments of
various parts in monsters ; but I doubt whether any of these
cases throw light on the origin of rudimentary organs in a state
of nature, further than by showing that rudiments can be
produced; for the balance of evidence clearly indicates that
species under nature do not undergo great and abrupt changes. But
we learn from the study of our domestic productions that the
disuse of parts leads to their reduced size ; and that the result is
inherited.

It appears probable that disuse has been the main agent in

Chap. XIV.] AND ABORTED ORGANS. 401

rendering organs rudimentary. It would at first lead by slow steps
to the more and more complete reduction of a part, until at last it
became rudimentary, — as in tlie case of the eyes of animals in-
habiting dark caverns, and of the wings of birds inhabiting oceanic
islands, which have seldom been forced by beasts of prey to take
ilight, and have ultimately lost the power of flying. Again, an
organ, useful under certain conditions, might become injurious under
ethers, as with the wings of beetles living on small and exposed
islands ; and in this case natural selection will have aided in re-
ducing the organ, until it was rendered harmless and rudimentary.

Any change in structure and function, which can be effected by
small stages, is within the power of natural selection ; so that an
organ rendered, through changed habits of life, useless or injurious
for one purpose, might be modified and used for another purpose.
An organ might, also, be retained for one alone of its former
functions. Organs, originally formed by the aid of natural selec-
tion, when rendered useless may well be variable, for their vari-
ations can no longer be checked by natural selection. All this
agrees well with what we see under nature. Moreover, at whatever
period of life either disuse or selection reduces an organ, and this
will generally be when the being has come to maturity and has
to exert its full powers of action, the principle of inheritance at
corresponding ages will tend to reproduce the organ in its reduced
state at the same mature age, but will seldom affect it in the
■embryo. Thus we can understand the greater size of rudimentary
organs in the embryo relatively to the adjoining parts, and their
lesser relative size in the adult. If, for instance, the digit of
an adult animal was used less and less during many generations,
owing to some change of habits, or if an organ or gland was less
and less functionally exercised, we may infer that it would become
reduced in size in the adult descendants of this animal, but would
retain nearly its original standard of development in the embryo.

There remains, however, this difficulty. After an organ has
ceased being used, and has become in consequence much reduced,
how can it be still further reduced in size until the merest vestige
is left ; and how can it be finally quite obliterated ? It is scarcely
possible that disuse can go on producing any further effect after
the organ has once been rendered functionless. Some additional
■exxilanation is here requisite which I cannot give. If, for in-
stance, it could be proved that every part of the organisation tends
to vary in a greater degree towards diminution than towards aug-
mentation of size, then we should be able to understand how an organ
which has become useless would be rendered, independently of the

2 D

402 SUM3IARr. [Chap. XIY.

effects of disuse, rudimentary and would at last be wholly sup-
pressed ; for the variations towards diminished size would no longer
be checked by natural selection. The principle of the economy
of growth, explained in a former chapter, by which the materials
forming any part, if not useful to the possessor, are saved as far as
is possible, will perhaps come into play in rendering a useless part
rudimentary. But this principle will almost necessarily be con-
fined to the earlier stages of the process of reduction ; for we cannot
suppose that a minute papilla, for instance, representing in a male
flower the pistil of the female flower, and formed merely of cellular
tissue, could be further reduced or absorbed for the sake of econo-
mising nutriment.

Finally, as rudimentary organs, by whatever steps they may
have been degraded into their present useless condition, are the
record of a former state of things, and have been retained solely
through the power of inheritance, — we can understand, on the
genealogical view of classification, how it is that systematists, itt
placing organisms in their proper places in the natural system, havt
often found rudimentary parts as useful as, or even sometimes more-
useful than, parts of high physiological importance. Kudimentary
organs may be compared with the letters in a word, still retained
in the spelling, but become useless in the pronunciation, but whichi
s-3rve as a clue for its derivation. On the view of descent with
modification, we may conclude that the existence of organs in a.
rudimentary, imperfect, and useless condition, or quite aborted, far
from presenting a strange difficulty, as they assuredly do on the old
doctrine of creation, might even have been anticipated in accordance-
with the views here explained.

Summary.

In this chapter I have attempted to show, that the arrangement
of all organic beings throughout all time in groups under groups —
"^Jiat the nature of the relationships by which all living and extinct
organisms are united by complex, radiating, and circuitous lines of
affinities into a few grand classes, — the rules followed and the
difficulties encountered by naturalists in their classifications, —
the value set upon characters, if constant and prevalent, whether
of high or of the most trifling importance, or, as with rudimentary
organs, of no importance, — the wide opposition in value between
analogical or adaptive characters, and characters of true, affinity;;
and other such rules ; — all naturally follow if we admit the common
parentage of allied forms, together with their modification through
variation and natural selection, with the contingencies of extinction;

Chap. XIV.] SUMMARY. 403

and divergence of character. In considering this view of classifica-
tion, it should be borne in mind that the element of descent has
been universally used in ranking together the sexes, ages, dimorphic
forms, and acknowledged varieties of the same species, however
much they may differ from each other in structure. If we extend
the use of this element of descent, — the one certainly known cause
of similarity in organic beings, — we shall understand what is mean -
by the Natural System : it is genealogical in its attempted arrange-
ment, with the grades of acquired difference marked by the terms,
varieties, species, genera, families, orders, and classes.

On this same view of descent with modification, most of the
great facts in Morphology become intelligible, — whether we look
to the same pattern displayed by the different species of the same
class in their homologous organs, to whatever purpose applied ;
or to the serial and lateral homologies in each individual animal
and plant.

On the principle of successive slight variations, not necessarily
or generally supervening at a very early period of life, and being
inherited at a corresponding period, we can understand the leading
facts in Embryology ; namely, the close rc-semblance in the indi-
vidual embryo of the parts which are homologous, and which when
matured become widely different in structurfi and function; and
the resemblance of the homologous parts or organs m allied though
distinct species, though fitted in the adult state for habits as
different as is possible. Larvae are active embryos, which have
been specially modified in a greater or less degree in relation to their
habits of life, with their modifications inherited at a correspond-
ing early age. On these same principles, — and bearing in mind,
that when organs are reduced in size, either from disuse or through
natural selection, it will generally be at that period of life when
the being has to provide for its own wants, and bearing in mind
how strong is the force of inheritance — the occurrence of rudi-
mentary organs might even have been anticipated. The im-
portance of embryological characters and of rudimentary organs
in classification is intelligible, on the view that a natural arrange-
ment must be genealogical.

Finally, the several classes of facts which have been considered
in this chapter, seem to me to proclaim so plainly, that the innu>
merable species, genera and families, with which this world ia
peopled, are all descended, each within its own class or group, from
common parents, and have all been modified in the course of descent,
that I should without hesitation adopt this view, even if it were
unsupported by other facts or arguments,

2 D 2

^04 RECAPITULATION. [Chap. XV.

CHAPTER XV

IvECAPITULATION AND CONCLUSION,

Recapitulation of the objections to the theory of Natural Selection — •
Recapitulation of the general and special circumstances in its favour
— Causes of the general belief in the immutability of species — How
far the theory of Natural Selection may be extended — Effects of its
adoption on the study of Natural History — Concluding remarks.

As this whole volume is one long argument, it may be convenient
to the reader to have the leading facts and inferences briefly re-
3apitulated.

That many and serious objections may be advanced against the
theory of descent with modification through variation and natural
selection, I do not deny. I have endeavoiired to give to them their
full force. Nothing at first can appear more difficult to believe than
that the more complex organs and instincts have been perfected,
not by means superior to, though analogous with, human reason,
but by the accumulation of innumerable slight variations, each good
for the individual possessor. Nevertheless, this difficulty, though
appearing to our imagination insuperably great, cannot be con-
sidered real if we admit the ibUowiagj^iopositi^s, namely, that
all parts of the organisation and instincts offer, at least, individual
differences — that there is a struggle for existence leading to the
preservation of profitable deviations of structure or instinct — and,
lastly, that gradations in the state of perfection of each organ may
have existed, each good of its kind. The truth of these propositions
-cannot, I think, be disputed.

It is, no doubt, extremely difficult even to conjecture by what
gradations many structures have been perfected, more especially
amongst broken and failing groups of organic beings, which have
suffered much extinction ; but we see so many strange gradations
in nature, that we ought to be extremely cautious in saying that
any organ or instinct, or any whole structure, could not have
arrived at its present state by many graduated steps. There are,
it must be admitted, cases of special difficulty opposed to the
theory of natural selection ; and one of the most curious of thesa

Chap. XV.] RECAPITULATION.

is the existence in the same community of two or three defined
castes of workers or sterile female ants ; but I have attempted
to show how these difficulties can be mastered.

With respect to the almost universal sterility of species when
first crossed, which forms so remarkable a contrast with the almost
universal fertility of varieties when crossed, I must refei" the reader
to the recapitulation of the facts given at the end of the ninth
chapter, which seem to me conclusively to show that this sterility
is no more a special endowment than is the incapacity of two
distinct kinds of trees to be grafted together ; but that it is
incidental on differences confined to the reproductive systems of
the intercrossed species. We see tiie truth of this conclusion in
the vast difference in the results of crossing the same two species
reciprocally, — that is, when one species is first used as the father
and then as the mother. Analogy from the consideration of
dimorphic and trimorphic plants clearly leads to the same con-
clusion, for when the forms are illegitimately united, they yield
few or no seed, and their offspring are more or less sterile ; and
these forms belong to the same undoubted species, and differ from
each other in no respect except in their reproductive organs and
functions.

Although the fertility of varieties when intercrossed and of their
mongrel offspring has been asserted by so many authors to be
universal, this cannot be considered as quite correct after the facts
given on the high authority of Gartner and Kolreuter. Most of
the varieties which have been experimented on have been pro-
duced under domestication ; and as domestication (I do not mean
mere confinement) almost certainly tends to eliminate that sterility
which, judging from analogy, would have affected the parent-species
if intercrossed, we ought not to expect that domestication would
likewise induce sterility in their modified descendants when crossed.
This elimination of sterility apparently follows from the same
cause which allows our domestic animals to breed freely under
diversified circumstances ; and this again apparently follows from
their having been gradually accustomed to frequent changes in
their conditions of life.

A double and parallel series of facts seems to throw much light
on the sterility of species, when first crossed, and of their hybrid
offspring. On the one side, there is good reason to believe that
slight changes in the conditions of life give vigour and fertility to all
organic beings. We know also that a cross between the distinct
individuals of the same variety, and between distinct varieties^
increases the number of their offspring, and certainly gives to them

406 RECAPITULATION. [Chap. XV.

increased size and vigour. This is chiefly owing to the forms which
are crossed having been exposed to somewhat different conditions
of life ; for I have ascertained by a laborious series of experiments
that if all the individuals of the same variety be subjected during
several generations to the same conditions, the good derived from
crossing is often much diminished or wholly disappears. This is
one side of the case. On the other side, we know that species
which have long been exposed to nearly uniform conditions, when
they are subjected under confinement to new and greatly changed
conditions, either perish, or if they survive, are rendered sterile,
though retaining perfect health. This does not occur, or only in a
very slight degree, with our domesticated productions, which have
long been exposed to fluctuating conditions. Hence, when we find
that hybrids produced by a cross between two distinct species arc
few in number, owing to their perishing soon after conception or
at a very early age, or if surviving that they are rendered more
or less sterile, it seems highly probable that this result is due to
their having been in fact subjected to a great change in their
conditions of life, from being compounded of two distinct organisa-
tions. He who will explain in a definite manner why, for instance,
an elephant or a fox will not breed under confinement in its native
country, whilst the domestic pig or dog will breed freely under the
most diversified conditions, will at the same time be able to give a
definite answer to the question why two distinct species, when
crossed, as well as their hybrid offspring, are generally rendered
more or less sterile, whilst two domesticated varieties when crossed
and their mongrel offspring are perfectly fertile.

Turning to geographical distribution, the difficulties encountered
on the theory of descent with modification are serious enough.
All the individuals of the same species, and all the species of the
same genus, or even higher group, are descended from common
parents ; and therefore, in however distant and isolated parts of the
world they may now be found, they must in the course of successive
gensrations have travelled from some one point to all the others.
We are often wholly unable even to conjecture how this could
have been effected. Yet, as we have reason to believe that some
species have retained the same specific form for very long periods
of time, immensely long as measured by years, too much stress
ought not to be laid on the occasional wide diffusion of the same
species ; for during very long periods there will always have been
a good chance for wide migration by many means. A broken
or interrupted range may often be accounted for by the extinction
of the species in the intermediate regions., It cannot be denied

Chap. XV.] RECAPITULATION. 407

that we are as yet very ignorant as to the full extent of the various
climatal and geographical changes which have affected the earth
during modern periods ; and such changes will often have facilitated
migration. As an example, I have attempted to show how potent
has heen the influence of the Glacial period on the distribution of
the same and of allied species throughout the world. We are as
yet profoundly ignorant of the many occasional means of trans-
port. With respect to distinct species of the same genus inha-
biting distant and isolated regions, as the process of modification
has necessarily been slow, all the means of migration will have
been possible during a very long period ; and consequently the
difficulty of the wide diffusion of the species of the same genus
is in some degree lessened.

As according to the theory of natural selection an interminable
number of intermediate forms must have existed, linking together
all the species in each group by gradations as fine as are our
existing varieties, it may be asked, Why do we not see these
linking forms all around us? Why are not all organic beings
blended together in an inextricable chaos? With respect to
existing forms, we should remember that we have no right to ex-
pect (excepting in rare cases) to discover directly connecting links
between them, but only between each and some extinct and sup-
planted form. Even on a wide area, which has during a long
period remained continuous,, and of which the climatic and other
conditions of life change insensibly in proceeding from a district
occupied by one species into another district occupied by a closely
allied species, we have no just right to expect often to find inter-
mediate varieties in the intermediate zones. For we have reason
to believe that only a few species of a genus ever undergo change ;
the other species becoming utterly extinct and leaving no modified
progeny. Of the species which do change, only a few within the
same country change at the same time; and all modifications
are slowly effected. I have also shown that the intermediate
varieties which probably at first existed in the intermediate zones,
would be liable to be supplanted by the allied forms on either
hand ; for the latter, from existing in greater numbers, would
generally be modified and improved at a q;uicker rate than the
intermediate varieties, which existed in lesser numbers ; so that
the intermediate varieties would, in the long run, be supplanted
and exterminated.

On this doctrine of the extermination of an infinitude of con-
necting links, between the living and extinct inhabitants of the
world, and at each euccessive period between the extinct and stiJl

408 RECAPITULATION. [Chap. XV,

older species, why is not every geological formation charged witli
such links? Why does not every collection of fossil remains
afford plain evidence of the gradation and mutation of the forms
of life ? Although geological research has undoubtedly revealed
the former existence of many links, bringing numerous forms
of life much closer together, it does not yield the infinitely many
fine gradations between past and present species required on the
theory ; and this is the most obvious of the many objections which
may be urged against it. Why, again, do whole groups of allied
species appear, though this appearance is often false, to have come
in suddenly on the successive geological stages? Although we
now know that organic beings appeared on this globe, at a period
incalculably remote, long before the lowest bed of the Cambrian
system was deposited, why do we not find beneath this system
great piles of strata stored with the remains of the progenitors of
the Cambrian fossils ? For on the theory, such strata must some-
where have been deposited at these ancient and utterly unknown
epochs of the world's history.

I can answer these questions and objections only on the sup-
position that the geological record is far more imperfect than most
geologists believe. The number of specimens in all our museums
is absolutely as nothing compared with the countless generations
of countless species which have certainly existed. The parent-
form of any two or more species would not be in all its characters
directly intermediate between its modified offspring, any more than
the rock-pigeon is directly intermediate in crop and tail between
its descendants, the pouter and fantail pigeons. We should not be
able to recognise a species as the parent of another and modified
species, if we were to examine the two ever so closely, unless we
possessed most of the intermediate links ; and owing to the imper-
fection of the geological record, we have no just right to expect
to find so many links. If two or three, or even more linking forms
were discovered, they would simply be ranked by many naturalists
as so many new species, more especially if found in different geo-
logical sub-stages, let their differences be ever so slight. Numerous
existing doubtful forms could be named which are probably varie-
ties ; but who will pretend that in future ages so many fossil links
will be discovered, that naturalists will be able to decide whether
or not these doubtful forms ought to be called varieties ? Only a
small portion of the world has been geologically explored. Only
organic beings of certain classes can be preserved in a fossil con-
dition, at least in any great number. Many species when once
formed never undergo any further change but become extinct

Chap. XV.] RECAPITULATION. 409

without leaving modified descendants; and the periods, during
which species have undergone modification, though long as mea-
sured by years, have probably been short in comparison with the
periods during which they retained the same form. It is the domi-
nant and widely ranging species which vary most frequently and
vary most, and varieties are often at first local — both causes
rendering the discovery of intermediate links in any one formation
less likely. Local varieties will not spiead into other and distant
regions until they are considerably modified and improved ; and
when they have spread, and are discovered in a geological forma-
tion, they appear as if suddenly created there, and will be simply
classed as new species. Most formations have been intermittent in
their accumulation ; and their duration has probably been shorter
than the average duration of specific forms. Successive formations
are in most cases separated from each other by blank intervals
of time of great length ; for fossiliferous formations thick enough
to resist future degradation can as a general rule be accumulated
only where much sediment is deposited on the subsiding bed of the
sea. During the alternate periods of elevation and of stationary
level the record will generally be blank. During tliese latter
periods there will probably be more variability in the forms of life ;
during periods of subsidence, more extinction.
^ With respect to the absence of strata rich in fossils beneath ths
Cambrian formation, I can recur only to the hypothesis given in
the tenth chapter ; namely, that though our continents and oceans
have endured for an enormous period in nearly their present relative
positions, we have no reason to assume that this has always been
the case ; consequently formations much older than any now
known may lie buried beneath the great oceans. With respect
to the lapse of time not having been sufficient since our planet
was consolidated for the assumed amount of organic change, and
this objection, as urged by Sir William Thompson, is probably one
of the gravest as yet advanced, 1 can only say, firstly, that we do
not know at what rate species change as measured by years, and
secondly, that many philosophers are not as yet willing to admit
that we know enough of the constitution of the universe and of
the interior of our globe to speculate with safety on its past dura-
tion.

That the geological record is imperfect all will admit ; but that
it is imperfect to the degree required by our theory, few will be
inclined to admit. If we look to long enough intervals of time,
geology plainh' declares that species have all changed ; and they
have changed in the manner required by tne theory, for they have

410 RECAPITULATION. [Chap. XV.

changed slowly and in a graduated manner. We clearly see this
in the fossil remains from consecutive formations invariably being
much more closely related to each other, than are the fossils from
widely separated formations.

Such is the sum of the several chief objections and difficulties
which may be justly urged against the theory; and I have now
briefly recapitulated the answers and explanations which, as far
as I can see, may be given. I have felt these difficulties far too
heavily during many years to doubt their weight. But it deserves
especial notice that the more important objections relate to ques-
tions on which we are confessedly ignorant ; nor do we know how
ignorant we are. We do not know all the possible transitional
gradations between the simplest and the most perfect organs; it
cannot be pretended that we know all the varied means of Distribu-
tion during the long lapse of years, or that we know how imperfect
IS the Geological Eecord. Serious as these several objections are,
in my judgment they are by no means sufficient to overthrow the
theory of descent with subsequent modification.

Now let us turn to the other side of the argument. Under
domestication we see much variability, caused, or at least excited,
by changed conditions of life ; but often in so obscure a manner,
that we are tempted to consider the variations as spontaneous.
Variability is governed by many complex laws, — by correlated
growth, compensation, the increased use and disuse of parts, and
the definite action of the surrounding conditions. There is much
difficulty in ascertaining how largely our domestic productions
have been modified ; but we may safely infer that the amount
has been large, and that modifications can be inherited for long
periods. As long as the conditions of life remain the same, we
have reason to believe that a modification, which has already been
inherited for many generations, may continue to be inherited for an
almost infinite number of generations. On the other hand, we have
evidence that variability when it has once come into play, does not
cease under domestication for a very long period ; nor do we know
that it ever ceases, for new varieties are still occasionally produced
by our oldest domesticated ^jroductions.

Variability is not actually caused by man; he only uninten-
tionally exposes organic beings to new conditions of life, and then
nature acts on the organisation and cause? i^ to vary. But man
can and does select the variations given to him by nature, <ind tnus
accumulates them in any desired manner. He thus adapts animals
and plants for his own benefit or pleasure. He may do this

€hap. XV.] RECAPITULATIO^. til

niethodically, or lie may do it unconsciously by preserving the
individuals most useful or pleasing to him without any intention of
altering the breed. It is certain that he can largely influence the
character of a breed by selecting, in each successive generation,
individual differences so slight as to be inappreciable except by an
educated eye. This unconscious process of selection has been the
great agency in the formation of the most distinct and useful
domestic breeds. That many breeds produced by man have to a
large extent the character of natural species, is shown by the
inextricable doubts whether many of them are varieties or aborigi-
nally distinct species.

There is no reason why the principles which have acted so
efficiently under domestication should not have acted under nature.
In the survival of favoured individuals and races, during the
constantly-recurrent Struggle for Existence, we see a powerful and
'Cver-acting form of Selection. The struggle for existence inevitably
follows from the high geometrical ratio of increase which is common
to all organic beings. This high rate of increase is proved by
calculation, — by the rapid increase of many animals and plants
during a succession of peculiar seasons, and when naturahsed in
new countries. More individuals are born than can possibly
survive. A grain in the balance may determine which individuals
shall live and which shall die, — which variety or species shall
increase in number, and which shall decrease, or finally become
extinct. As the individuals of the same species come in all
respects into the closest competition with each other, the struggle
will generally be most severe between them; it will be almost
equally severe between the varieties of the same species, and next
in severity between the species of the same genus. On the other
hand the struggle will often be severe between beings remote in the
scale of nature. The slightest advantage in certain individuals, at
any age or during any season, over those with which they come
into competition, or better adaptation in however slight a degree to
the surrounding physical conditions, will, in the long run, turn the
balance.

With animals having separated sexes, there will be in most cases
a struggle between the males for the possession of the females.
The most vigorous males, or those which have most successfully
struggled with their conditions of life, will generally leave most
progeny. But success will often depend on the males having
special weapons, or means of defence, or charms; and a slight
advantage will lead to victory.

As 2;eology plainly proclaims that each land has undergone great

412 RECAPITULATION. [Chap. XV.

physical changes, we might have expected to find that organic,
beings have varied under nature, in the same way as they have
varied under domestication. And if there has been any variabihty
under nature, it would be an unaccountable fact if natural selection
had not come into play. It has often been asserted, but the
assertion is incapable of proof, that the amount of variation under
nature is a strictly limited quantity. Man, though acting on
external characters alone and often capriciously, can produce within
a short period a great result by adding up mere individual differences
in his domestic productions; and every one admits that species
present individual differences. But, besides such differences, all
naturalists admit that natural varieties exist, which arc considered
sufficiently distinct to be woilhy of record in systematic works.
No on-e has drawn any clear distinction between individual differ-
ences and slight varieties ; or between more plainly marked varieties
and sub-species, and species. On separate continents, and on
different parts of the same continent when divided by barriers of
any kind, and on outlying islands, what a multitude of forms exists
which some experienced naturalists rank as varieties, others a>
geographical races or sub-species, and others as distinct, though
closely allied species !

If then, animals and plants do vary, let it be ever so slightly or
slowly, why should not variations or individual differences, which
are in any way beneficial, be preserved and accumulated through
natural selection, or the survival of the fittest? IX_inan_caiiby
j^atience select variations useful to him, why, under changing^and
complex conditions of life, should not variations useful to nature's
living products often arise, and be preserved or selected? What
limit can be put to this power, acting during long ages and rigidly
scrutinising the whole constitution, structure, and habits of each
creature, — favouring the good and rejecting the bad ? I can see no
limit to this power, in slowly and beautifully adapting each form to
the most complex relations of life. The theory of natural selection,
even if we look no farther than this seerns to be in the highest
degrea^probable. I have already recapitulated, as fairly as I could,
the opposed difficulties and objections: now let us turn to the
special facts and arguments in favour of the theory.

On the view that species are only strongly marked and permanent
varieties, and that each species first existed as a variety, we can
see why it is that no line of demarcation car. be drawn between
species, commonly supposed to have been produced by special acts
•:f creation, and vai'ieties which are acknowledged to have been

Chap. XV.] r.ECAPITULATlON. 413

produced by secondary laws. On this same view we can understand
how it is that in a region where many species of a genus have been
produced, and where they now flourish, these same species should
present many varieties ; for where the manufactory of species has
been active, we might expect, as a general rule, to find it still in
action ; and this is the case if varieties be incipient species. More-
over, the species of the larger genera, which afford the greater
number of varieties or incipient species, retain to a certain degree
the character of varieties ; for they differ from each other by a less
amount of difference than do the species of smaller genera. The
closely allied species also of the larger genera apparently have re-
stricted ranges, and in their affinities they are clustered in little groups
round other species — in both respects resembling varieties. These
are strange relations on the view that each species was independently
created, but are intelligible if each existed first as a variety.

As each species tends by its geometrical rate of reproduction to
increase inordinately in number ; and as the modified descendants
of each species will be enabled to increase by as much as they
become more diversified in habits and structure, so as to be able
to seize on many and widely different places in the economy of
nature> there will be a constant tendency in natural selection to
preserve the most divergent offspring of any one species. Hence,
during a long-continued course of modification, the slight differences
characteristic of varieties of the same species, tend to be augmented
into the greater differences characteristic of the species of the same
genus. New and improved varieties will inevitably supplant and
exterminate the cider, less improved, and intermediate varieties;
and thus species are rendered to a large extent defined and
distinct objects. Dominant species belonging to the larger
groups within each class tend to give birth to new and domi-
nant forms ; so that each large group tends to become still
larger, and at the same time more divergent in character. But as
all groups cannot thus go on increasing in size, for the world would
not hold them, the more dominant groups beat the less dominant.
This tendency in the large groups to go on increasing in size and
diverging in character, together with the inevitable contingency of
much extinction, explains the arrangement of all the forms of life
in groups subordinate to groups, all within a few great classes,
which has prevailed throughout all time. This grand fact of the
grouping of all organic beings under what is called the Natural
System, is utterly inexplicable on the theory of creation.

As natural selection acts solely by accumulating slight, successive,
favourable variations, it can produce no great or sudden modifica-

414 RECAPITULATIOX. [Chap. XV.

tions ; it can act only by short and slow steps. . Hence the canon of
"Natura ncn facit saltum," which every fresh addition to our
knowledge tends to confirm, is on this theory intelligible. We can
see why throughout nature the same general end is gained by an
almost infinite diversity of means, for every peculiarity when once
acquired is long inherited, and structures already modified in many
different ways have to be adapted for the same general purpose. We
can, in short, see why nature is prodigal in variety, though niggard
in innovation. But why this should be a law of nature if each
species has been independently created, no man can explain.

Many other facts are, as it seems to me, explicable on this theory.
How strange it is that a bird, under the form of a woodpecker,,
should prey on insects on the ground; that upland geese which
rarely or never swim, should possess webbed feet ; that a thrush-
like bird should dive and feed on sub-aquatic insects ; and that a
petrel should have the habits and structure fitting it for the life of
an auk ! and so in endless other cases. But on the view of each
species constantly trying to increase in number, with natural
selection always ready to adapt the slowly varying descendants of
each to any unoccupied or ill-occupied place in nature, these facts
cease to be strange, or might even have been anticipated.

We can to a certain extent understand how it is that there is
so much beauty throughout nature ; for this may be largely attri-
buted to the agency of selection. That beauty, according to our
sense of it, is not universal, must be admitted by every one who
will look at some venomous snakes, at some fishes, and at certain
hideous bats with a distorted resemblance to the human face.
Sexual selection has given the most brilliant colours, elegant
patterns, and other ornaments to the males, and sometimes to
both sexes of many birds, butterflies, and other animals. With
birds it has often rendered the voice of the male musical to the
female, as well as to our ears. Flowers and fruit have been
rendered conspicuous by brilliant colours in contrast with the green
foliage, in order that the flowers may be easily seen, visited, and
fertilised by insects, and the seeds disseminated by birds. How it
comes that certain colours, sounds, and forms should give pleasure
to man and the lower animals,— that is, how the sense of beauty
in its simplest form was first acquired, — we do not know any
more than how certain odours and flavours were first rendered
agreeable.

As natural selection acts by competition, it adapts and improves
the inhabitants of each country only in relation to their co-
inhabitants ; so that we need feel no surprise at the species of any

CuAP. XV.] RECAPITULAIION. 415

one country, although on the ordinary view supposed to have need
created and specially adapted for that country, being beaten and
supplanted by the naturalised productions from another land. Nor
ought we to marvel if all the contrivances in nature be not, as far
as we can judge, absolutely perfect, as in the case even of the
human eye ; or if some of them be abhorrent to our ideas of
fitness. We need not marvel at the sting of the bee, when used
against an enemy, causing the bee's own death ; at drones being
produced in such great numbers for one single act, and being then
slaughtered by their sterile sisters; at the astonishing waste of
pollen by our fir-trees ; at the instinctive hatred of the queen-bee
for her own fertile daughters ; at ichneumonidse feeding within the
living bodies of caterpillars ; or at other such cases. The wonder
indeed is, on the theory of natural selection, that more cases of the
want of absolute perfection have not been detected.

The complex and little known laws governing the production
of varieties are the same, as far as we can judge, with the laws
which have governed the production of distinct species. In both
cases physical conditions seem to have produced some direct
and definite effect, but how much we cannot say. Thus, when
varieties enter any new station, they occasionally assume some of
the characters proper to the species of that station. With both
varieties and species, use and disuse seem to have produced a
considerable effect; for it is impossible to resist this conclusion
when we look, for instance, at the logger-headed duck, which has
wings incapable of flight, in nearly the same condition as in the
domestic duck ; or when we look at the burrowing tucu-tucu, which
is occasionally blind, and then at certain moles, which are habitually
blind and have their eyes covered with skin ; or when we look
at the blind animals inhabiting the dark caves of America and
Europe. With varieties and species, correlated variation seems to
have played an important part, so that when one part has been
modified other parts have been necessarily modified. With hoib.
varieties and species, reversions to long-lost characters occasionally
occur. How inexplicable on the theory of creation is the occasional
appearance of stripes on the shoulders and legs of the several species
of the horse-genus and of their hybrids ! How simply is this fact

'explained if we believe that these species are all descended from a
striped progenitor, in the same manner as the several domestic
breeds of the pigeon are descended from the blue and barred rock-
pigeon !

On the ordinary view of each species having been independently

; created, why should specific characters, or those by which the

416 RECAPITULATION [Chap. XV.

species of the same genus differ from each other, be more variable
than generic characters in which they all agree? Why, for in-
stance, should the colour of a flower be more likely to vary in
any one species of a genus, if the other species possess differently
coloured flowers, than if all possessed the same coloured flowers ?
If species are only well-marked varieties, of which the characters
have become in a high degree permanent, we can understand this
fact ; for they have already varied since they branched off from a
common progenitor in certain characters, by which they have come
to be specifically distinct from each other ; therefore these same
characters would be more likely again to vary than the generic cha-
racters which have been inherited without change for an immense
I)eriod. It is inexplicable on the theory of creation why a part
developed in a very unusual manner in one species alone of a genus,
and therefore, as we may naturally infer, of great importance to
that species, should be eminently liable to variation ; but, on our
view, this part has undergone, since the several species branched off
from a common progenitor, an unusual amount of variability and
modification, and therefore we might expect the part generally to
be still variable. But a part may be developed in the most unusual
manner, like the wing of a bat, and yet not be more variable than
any other structure, if the part be common to many subordinate
forms, that is, if it has been inherited for a very long period ; for in
this case it will have been rendered constant by long-continued
natural selection.

Glancing at instincts, marvellous as some are, they offer no
greater difficulty than do corporeal structures on the theory of the
natural selection of successive, slight, but profitable modifications.
We can thus understand why nature moves by e;raduated steps in
endowing different animals of the same class with their several
instincts. I have attempted to show how much light the principle
of gradation throws on the admirable architectural powers of the
hive-bee. Habit no doubt often comes into play in modifying
instincts; but it certainly is not indispensable, as we see in the
case of neuter insects, which leave no progeny to inherit the effects
of long-continued habit. On the view of all the species of the same
genus having descended from a common parent, and having in-
herited much in common, we can understand how it is that allied
species, when placed under widely different conditions of life, yet
follow nearly the same instincts ; why the thrushes of tropical and
temperate South America, for instance, line their nests with mud
like our British species. On the view of instincts having been
slowly acquired through natural selection, we need not marvel

i

(^iiAP. XV.] RECAPJTULATION. 417

at some instincts being not perfect and liable to mistakes, and at
many instincts causing other animals to suffer.

If species be only well-marked and permanent varieties, we can
at once see why their crossed ofispring should follow the same
complex laws in their degrees and kinds of resemblance to their
parents, — in being absorbed into each other by successive crosses,
and in other such points, — as do the crossed offspring of acknow-
ledged varieties. This similarity would be a strange fact, if species
had been independently created and varieties had been produced
through secondary laws.

If we admit that the geological record is imperfect to an extreme
degree, then the facts, which the record does give, strongly support
the theory of descent with modification. New species have come
on the stage slowly and at successive intervals ; and the amount of
change, after equal intervals of time, is widely dififerent in diiferent
groups. The extinction of species and of whole groups of species,
which has played so conspicuous a part in the history of the
organic world, almost inevitably follows from the principle o(
natural selection ; for old forms are supplanted by new and im-
proved forms. Neither single species nor groups of species re-
appear when the chain of ordinary generation is once broken. The
gradual diffusion of dominant forms, with the slow modification oi
their descendants, causes the forms of life, after long intervals
of time, to appear as if they had changed simultaneously through-
out the world. The fact of the fossil remains of each formation
being in some degree intermediate in character between the fossils
in the formations above and below, is simply explained by their
intermediate position in the chain of descent. The grand fact
that all extinct beings can be classed with all recent beings,
naturally follows from the living and the extinct being the off-
spring of common parents. As species have generally diverged in
character during their long course of descent and modification, wo
can understand why it is that the more ancient forms, or early
progenitors of each group, so often occupy a position in some
degree intermediate between existing groups. Kecent forms are
generally looked upon as being, on the whole, higher in the scale
of organisation than ancient forms ; and they must be higher, in
so far as the later and more improved forms have conquered the
' older and less improved forms in the struggle for life ; they have
also generally had their organs more specialised for dififerent
functions. This fact is perfectly compatible with numerous beings
still retaining simple and but little improved structures, fitted for
simple conditions of life ; it is likewise compatible with some

2 E

418 RECAPITULATION. [Chap. XV.

forms having retrograded in organisation, by having become at
each stage of descent better fitted for new and degraded habits
of life. Lastly, the wonderful law of the long endurance of allied
forms on the same continent, — of marsupials in Australia, of eden-
tata in America, and other such cases, — is intelligible, for within
the same country the existing and the extinct will be closely
allied by descent.

Looking to geographical distribution, if we admit that there has
been during the long course of ages much migration from one part
of the world to another, owing to former climatal and geographical
changes and to the many occasional and unknown means of dis-
persal, then we can understand, on the theory of descent with
modification, most of the great leading facts in Distribution. "\Vo
can see why there should be so striking a parallelism in the dis-
tribution of organic beings throughout space, and in their geological
succession throughout time ; for in both cases the beings have been
connected by the bond of ordinary generation, and the means of
modification have been the same. We see the full meaning of the
wonderful fact, which has struck every traveller, namely, that on
the same continent, under the most diverse conditions, under heat
and cold, on mountain and lowland, on deserts and marshes, most
of the inhabitants within each great class are plainly related ; for
they are the descendants of the same progenitors and early colonists.
On this same principle of former migration, combined in most cases
with modification, we can understand, by the aid of the Glacial
period, the identity of some few plants, and the close alliance of
many others, on the most distant mountains, and in the northern
and southern temperate zones ; and likewise the close alliance of
some of the inhabitants of the sea in the northern and southern
temperate latitudes, though separated by the whole intertropical
ocean. Although two countries may present physical conditions
as closely similar as the same species ever require, we need feel no
surprise at their inhabitants being widely different, if they have
been for a long period completely sundered from each other ; for as
the relation of organism to organism is the most important of all
relations, and as the two countries will have received colonists
at various periods and in different proportions, from some other
country or from each other, the course of modification in the two
areas will inevitably have been different.

On this view of migration, with subsequent modification, we
see why oceanic islands are inhabited by only few species, but of
these, why many are peculiar or endemic forms. We ckarlj see
why species belonging to those groups of animals which cannot

Chap. XV.] RECAPITULATION. 419

cross wide spaces of the ocean, as frogs and terrestrial mammals, do
not inhabit oceanic islands; and why, on the other hand, new and
peculiar species of bats, animals which can traverse the ocean, are
often found on islands far distant from any continent. Such cases
as the presence of peculiar species of bats on oceanic islands and
the absence of all other terrestrial mammals, are facts utterly
inexplicable on the theory of independent acts of creation.

The existence of closely allied or representative species in any
two areas, implies, on the theory of descent with modification, that
the same parent-forms formerly inhabited both areas : and we
almost invariably find that wherever many closely allied species
inhabit two areas, some identical species are still common to both.
Wherever many closely allied yet distinct species occur, doubtful
forms and varieties belonging to the same groups likewise occur,
It is a rule of high generality that the inhabitants of each area are
related to the inhabitants of the nearest source whence immigrants
might have been derived. We see this in the striking relation ot
nearly all the plants and animals of the Galapagos archipelago,
of Juan Fernandez, and of the other American islands, to the
plants and animals of the neighbouring American mainland ; and
of those of the Cape de Verde archipelago, and of the other African
islands to the African mainland. It must be admitted that these
facts receive no explanation on the theory of creation.

The fact, as we have seen, that all past and present organic beings
■can be arranged within a few great classes, in groups subordinate to
groups, and with the extinct groups often falling in between the
rc^cent groups, is intelligible on the theory of natural selection with
its contingencies of extinction and divergence of character. On
these same principles we see how it is, that the mutual affinities of
the forms within each class are so complex and circuitous. We
see why certain characters are far more serviceable than others for
classification ; — why adaptive characters, though of paramount im-
portance to the beings, are of hardly any importance in classifi-
cation ; why characters derived from rudimentary parts, though of
iio service to the beings, are often of high classificatory value; and
why embryological characters are often the most valuable of all.
The real affinities of all organic beings, in contradistinction to their
adaptive resemblances, are due to inheritance or community of
descent. The Natural System is a genealogical arrangement, with
the acquired grades of difference, marked by the terms, varieties,
ei^ecies, genera, families, &c. ; and we have to discover the lines
cf descent by the most permanent characters whatever they may
be and of however slight vital importance.

2 E 2

I

420 RECAPITULATION. [Chap. XV.

The similar frcmework of boues in tTie hand of a man, wing o^
a bat, fin of tbe porpoise, and leg of the horse, — the same number
of vertebra) forming the neck of the giraffe and of the elephant, —
and innumerable other such facts, at once explain themselves on
the theory of descent with slow and slight successive modifica-
tions. The similarity of pattern in the wing and in the leg of
a bat, though used for such different purpose, — in the jaws and
legs of a crab,— in the petals, stamens, and pistils of a flower
is likewise, to a large extent, intelligible on the view of the
gradual modification of parts or organs, which were aboriginally
alike in an early progenitor in each of these classes. On the
principle of successive variations not always supervening at an
early age, and being inherited at a corresponding not early
period of life, we clearly see why the embryos of mammals,
birds, reptiles, and fishes should be so closely similar, and so
unlike the adult forms. We may cease marvelling at the em-
bryo of an air-breathing mammal or bird having branchial slits
ind arteries running in loops, like those of a fish which has to
oreathe the air dissolved in water by the aid of well-developed
branchise.

Disuse, aided sometimes by natural selection, will often have
reduced organs when rendered useless under changed habits or
:x)nditions of life ; and we can understand on this view the meaning
of rudimentary organs. But disuse and selection will generally act
on each creature, when it has come to maturity and has to play its
full part in the struggle for existence, and will thus have little
power on an organ during early life ; hence the organ will not be
reduced or rendered rudimentary at this early age. The calf, for
instance, has inherited teeth, which never cut through the gums of
the uipper jaw, from an early progenitor having well-developed
teeth ; and we may believe, that the teeth in the mature animal
were formerly reduced by disuse, owing to the tongue and palate,
or lips, having become excellently fitted through natural selection
td browse without their aid ; whereas in the calf, the teeth have
been left unaffected, and on the principle of inheritance at cor-
responding ages have been inherited from a remote period to
the present day. On the view of each organism with all its
separate parts having been specially created, how utterly inexplic-
able is it that organs bearing the plain stamp of inutility, such
as the teeth in the embryonic calf or the shrivelled wings under
the soldered wing-covers of many beetles, should so frequently
occur. Nature may be said to have taken pains to reveal her
scheme of modification, by means of rudimentary organs, of em-

Chap. XV.] CONCLUSION. 421

"bryological and homologous structures, but we are too blind to
luiderstand her meaning.

I have now recapitulated the facts and considerations which have
thoroughly convinced me that species have been modified, during a
long course of descent. This has been effected chiefly through the
natural selection of numerous successive, slight, favourable varia-
tions ; aided in an important manner by the inherited effects of the
use and disuse of parts ; and in an unimportant manner, that is
in relation to adaptive structures, whether past or present, by the
direct action of external conditions, and by variations v.'hich seem
to us in our ignorance to arise spontaneously. It appears that
I formerly underrated the frequency and value of these latter
forms of variation, as leading to permanent modifications of struc-
ture independently of natural selection. But as my conclusions
Iiave lately been much misrepresented, and it has been stated
that I attribute the modification of species exclusively to natural
selection, I may be permitted to remark that in the first edition of
this work, and subsequently, I placed in a most conspicuous posi-
tion— namely, at the close of the Introduction — the following words :
*-* I am convinced that natural selection has been the main but not
the exclusive means of modification." This has been of no avail.
Great is the power of steady misrepresentation; but the history
of science shows that fortunately this power does not long endure.

It can hardly be supposed that a false theory would explain, in
60 satisfactory a manner as does the theory of natural selection, the
several large classes of facts above specified. It has recently
been objected that this is an unsafe method of arguing; but
it is a method used in judging of the common events of life, and
has often been used by the greatest natural philosophers. The
undulatory theory of light has thus been arrived at ; and the belief
in the revolution of the earth on its own axis was until lately
supported by hardly any direct evidence. It is no valid objection
that science as yet throws no light on the far higher problem of the
essence or origin of life. Who can explain what is the essence of
the attraction of gravity ? No one now objects to following out the
•results consequent on this unknown element of attraction ; not-
withstanding that Leibnitz formerly accused Newton of introducing
■** occult qualities and miracles into philosophy."

I see no good reason why^the yiews given in this volume shoula
«hock the_ religious feelings of any one. It is satisfactory, as
showing how transient such impressions are, to remember that the
greatest discovery ever made by man, namely, the law of the

422 CONCLUSION. [Chap. XV.

sittraction of gravity, was also attacked by Leibnitz, "as sub-
versive of natural, and inferentially of revealed, religion." A cele-
brated author and divine has written to me that " he has gradually
" learnt to see that it is just as noble a conception of the Deity to
** believe that He created a few original forms capable of self-
" development into other and needful forms, as to believe that He
" required a fresh act of creation to su])ply the voids caused by the
** action of His laws."

Why, it may be asked, until recently did nearly all the most
eminent living naturalists and geologists disbelieve in the muta-
bility of species. It cannot be asserted that organic beings in a
state of nature are subject to no variation ; it cannot be proved
that the amount of variation in the course of long ages is a limited
quantity ; no clear distinction has been, or can be, drawn between
species and well-marked varieties. It cannot be maintained that
species when intercrossed are invariably sterile, and varieties in-
variably fertile ; or that sterility is a special endowment and sign
of creation. The belief that species were immutable productions
was almost unavoidable as long as the history of the world was
thought to be of short duration ; and now that we have acquired
some idea of the, lapse of time, we are too apt to assume, without
proof, that the geological record is so perfect that it would have
afforded us plain evidence of the mutation of species, if they had
undergone mutation.

But the chief cause of our natural unwillingness to admit that
one species has given birth to other and distinct species, is that we i
are always slow in admitting great changes of which we do not see
the steps. The difificulty is the same as that felt by so many geo-
logists, when Lyell first insisted that long lines of inland cliffs had
been formed, and great valleys excavated, by the agencies which
we see still at work. The mind cannot possibly grasp the full ,
meaning of the term ol even a million years ; it cannot add up and i
perceive the full effects of many slight variations, accumulated /
during an almost infinite number of generations. ... ..

Although I am fully convinced of the truth of the views given in
this volume under the form of an abstract, I by no means expect
to convince experienced naturalists whose minds are stocked with
a multitude of facts all viewed, during a long course of years, from
a point of view directly opposite to mine. It is so easy to hide our
ignorance under such expressions as the " plan of creation," " unicy
of design," &c., and to think that we give an explanation when wo
^ only re-state a fact. Any one whose disposition leads him to attach
more weight to unexplained difficulties than to the explanation of

Chap. XV.] CONCLUSION. 423

a certain number of facts will certainly reject the theory. A few
naturalists, endowed with much flexibility of mind, and who have
already begun to doubt the immutability of species, may be in-
fluenced by this volume ; but I look with confidence to the future, —
to young and rising naturalists, who will be able to view both sides
of the question with impartiality. Whoever is led to believe that
species are mutable will do good service by conscientiously ex-
pressing his conviction ; for thus only can the load of prejudice by
which this subject is overwhelmed be removed.

Several eminent naturalists have of late published their belief
that a multitude of reputed species in each genus are not real
species; but that other species are real, that is, have been inde-
pendently created. This seems to me a strange conclusion to
arrive at. They admit that a multitude of foims, which till lately
they themselves thought were special creations, and which are still
thus looked at by the majority of naturalists, and which conse-
quently have all the external characteristic features of true species,
— they admit that these have been produced by variation, but they
refuse to extend the »ame view to other and slightly different forms.
Nevertheless they do not pretend that they can define, or even
conjecture, which arc the created forms of life, and which are those
produced by secondary laws. They admit variation as a vera causa
in one case, they arbitrarily reject it in another, without assigning
any distinction in the two cases. The day will come when this
will be given as a curious illustration of the blindness of precon-
ceived opinion. These authors seem no more startled at a mira-
culous act of creation than at an ordinary birth. But do they
really believe that at innumerable periods in the earth's history
certain elemental atoms have been commanded suddenly to flash
into living tissues ? Do they believe that at each supposed act ot
creation one individual or many were produced? Were all the
infinitely numerous kinds of animals and plants created as eggs or
seed, or as full grown ? and in the case of mammals, were they
created bearing the false marks of nourishment from the mother's
womb ? UndoubleHTy some of these same questions cannot be
answered by those who believe in the appearance or creation of only
a few forms of life, or of some one form alone. It has been main-
tained by several authors that it is as easy to believe in the creation
of a million beings as of one; but Maupertuis' philosophical
axiom "of least action " leads the mind more willingly to admit
the smaller number ; and certainly we ought not to believe that,
innumerable beings within each great class have been created
with plain, but deceptive, marks of descent from a sin2;ie pawjnl.

'i24 CONCLUSION. [Chap. X^

As a record of a former state of things, I have retained in the-
foregoing paragraphs, and elsewhere, several sentences which imply-
that naturalists believe in the separate creation of each species ; and
[ have been much censured for having thus expressed myself.
But undoubtedly this was the general belief when the first
edition of the present work appeared. I formerly spoke to very
many naturalists on the subject of evolution, and never once met
with any sympathetic agreement. It is probable that some did
then believe in evolution, but they were either silent, or expressed
themselves so ambiguously that it was not easy to understand their
meaning. Now things are wholly changed, and almost every
naturalist admits the great principle of evolution. There are, how-
ever, some who still think that species have suddenly given birth,
through quite unexplained means, to new and totally different
forms : but, as I have attempted to show, weighty evidence can be
opposed to the admission of great and abrupt modifications. Under
a scientific point of view, and as leading to further investigation,
but little advantage is gained by believing that new forms are
suddenly developed in an inexplicable manner from old and widely
different forms, over the old belief in the creation of species from
the dust of the earth. ^

It may be asked how far I extend the doctrine of the modification
of species. The question is difficult to answer, because the more
distinct the forms are which we consider, by so much the arguments
in favour of community of descent become fewer in number and less
in force. But some arguments of the greatest weight extend very
far. All the members of whole classes are connected together by
a chain of affinities, and all can be classed on the same principle,
in groups subordinate to groups. Fossil remains sometimes tend
to fill up very wide intervals between existing orders.

Organs in a rudimentary condition plainly show that an early
progenitor had the organ in a fully developed condition ; and this
in some cases implies an enormous amount of modification in
the descendants. Throughout whole classes various structures are
Jbrmed on the same pattern, and at a very early age the embryos
closely resemble each other. Therefore I cannot doubt that the
theory of descent with modification embraces all the members of
the same great class or kingdom. I believe that animals are
descended from at most only four or five progenitors, and plants
from an equal or kesser number.

Analogy would lead me one step farther, namely, to the belief
that all animals and plants are descended from some one prototype.
But analogy may be a deceitful guide. Nevertheless all livinp

Chap. XV.] CONCLUSION. 426

things have much in common, in their chemical composition, their
cellular structure, their laws of gfowtS^ and their liability to lu-
lurious influences. We see this even in so trifling a fact *)s jhat tlu
same poison often similarly affects plants and anima^i , or thai
the poison secreted by the gall-fly produces monstrous growths
on the wild rose or oak-tree. With all organic beings, excepting
perhaps "^me of the very lowest, sexual reproduction seems to be
essentially similar. With all, as far as is at present known, the
germinal vesicle is the same ; so that all organisms start from a
common origin. If we look even to the two main divisions —
namely, t5rtK'e~animal and vegetable kingdoms — certain low forms
are so far intermediate in character that naturalists have disputed
to which kingdom they should be referred. As Prolessor Asa Gray
has remarked, " the spores and other reproductive bodies of many
*' of the lower algae may claim to have first a characteristically
" animal, and then an unequivocally vegetable existence." There-
fore, on the principle of natural selection with divergence of
character, it does not seem incredible that, from some such low and
intermediate form, both animals and plants may have been de-
veloped ; and, if we admit this, we must likewise admit that all
the organic beings which have ever lived on this earth may be
descended from some one primordial form. But this inference is
chiefly grounded on analogy, and it is immaterial whether or not
it be accepted. No doubt it is possible, as Mr. G. H. Lewes has
urged, that at the first commencement of life many different forms
were evolved ; but if so, we may conclude that only a very few
have left modified descendants. For, as I have recently remarked
in regard to the members of each great kingdom, such as the
Vertebrata, Articulata, &c., we have distinct evidence in their
embryological, homologous, and rudimentary structures, that
within each kingdom all the members are descended from a single
progenitor.

When the views advanced by me in this volume, and by Mr.
Wallace, or when analogous views on the origin of species are
generally admitted, we can dimly foresee that there will be a
considerable revolution in natural history. Systematists will be
able to pursue their labours as at present; but they will not be
incessantly haunted by the shadowy doubt whether this or that
form be a true species. This, I feel sure and I speak after experience,
will be no slight relief. The endless disputes whether or not some
fifty species of British brambles are good species will cease. Syste-
matists will have only to decide (not that this will be easy) whether
Biy form be sufficiently constant and distinct from other forms

426 CONCLUSION. [Chap. XV.

to he capable of definition ; and if definable, whether the differences
be sufficiently important to deserve a specific name. Th}s latter
point will become a far more essential consideration than it is at
present ; for differences, however slight, between any two forms,
if not blended by inteimediate gradations, are looked at by most
naturalists as sufficient to raise both forms to the rank of species.

Hereafter we shall be compelled to acknowledge that the only
distinction between species and well-marked varieties is, that the
latter are known, or believed, to be connected at the present day by
intermediate gradations, whereas species were formerly thus con-
nected. Hence, without rejecting the consideration of the present
existence of intermediate gradations between any two forms, we shall
be led to weigh more carefully and to value higher the actual
amount of difference between them. It is quite possible that forms
now generally acknowledged to be merely varieties may hereafter
be thought worthy of specific names ; and in this case scientific and
common language will come into accordance. In short, we shall
have to treat species in the same manner as those naturalists treat
genera, who admit that genera are merely artificial combinations
made for convenience. This may not be a cheering prospect ; but
we shall at least be freed from the vain search for the undiscovered
and undiscoverable essence of the term species.

The other and more general departments of natural history will
rise greatly in interest. The terms used by naturalists, of affinity,
relationship, community of type, paternity, morphology, adaptive
characters, rudimentary and aborted organs, &c., will cease to be
metaphorical, and will have a plain signification. When we no
longer look at an oiganic being as a savage looks at a ship, as some-
thing wholly beyond his comprehension ; when we regard every
production of nature as one which has had a long history ; when we
contemplate every complex structure and instinct as the summing
up of many contrivances, each useful to the possessor, in the same
way as any great mechanical invention is the summing up of the
labour, the experience, the reason, and even the blunders of nume-
rous workmen ; when we thus view each organic being, how far
more interesting, — I speak from experience, — does the study of
natural BisTory become !

A grand and almost untrodden field of inquiry will be opened, on
the causes and laws of variation, on correlation, on the effects of use
and disuse, on the direct action of external conditions, and so forth.
The study of domestic productions will rise immensely in value. A
new variety raised by man will be a more important and interesting
Butject fcr study than one more species added to tho infinitude of

Chap. XV.T CONCLUSION 427

already recorded species. Our classifications will come to be, as far
as they can be so made, genealogies ; and will then truly give what
n^'ty be called the plan of creation. The rules for classifying will
no doubt become simpler when we have a definite object in view.
We possess no pedigrees or armorial bearings ; and we have to dis-
cover and trace the many diverging lines of descent in our natural
genealogies, by characters of any kind which have long been in-
herited. Rudimentary organs will speak infallibly with respect to
the nature of long-lost structures. Species and groups of species
which are called aberrant, and which may fancifully be called living
fossils, will aid us in forming a picture of the ancient forms of life.
Embryology will often reveal to us the structure, in some degree
obscured, of the prototypes of each great class.

When we can feel assured that all the individuals of the same^
iipecies, and all the closely allied species of most genera, have within '
a not very remote period descended from one parent, and have
migrated from some one birth-place ; and when we better know
the many means of migration, then, by the light which geology
now throws, and will continue to throw, on former changes of
climate and of the level of the land, we shall surely be enabled to
trace in an admirable manner the former migrations of the inhabi-
tants of the whole world. Even at present, by comparing the
differences between the inhabitants of the sea on the opposite sides
of a continent, and the nature of the various inhabitants on that
continent in relation to their apparent means of immigration, some
light can be thjown on ancient^geography. ^ _^- -^_ _-^^ —

The noble science of Geology loses~^lory from the extreme X^
imperfection of the record. The crust of the earth with its em-
bedded remains must not be looked at as a well-filled museum, but
as a poor collection made at hazard and at rare intervals. The accu-
mulation of each great fossiliferous formation will be recognised as
having depended on an unusual concurrence of favourable circum-
stances, and the Iblank' intervals" between the successive stages as
having been of vast duration. But we shall be able to gauge with
some security the duration of these intervals by a comparison of
the preceding and succeeding organic forms. We must be cautious
in attempting to correlate as strictly coniemporaneous two forma-
tions, which do not include many identical species, by the general
succession of the forms of life. As species are produced and ex-
terminated by slowly acting and still existing causes, and not by
miraculous acts of creation ; and as the most important of all causes
of organic change is one which is almost independent of altered
and perhaps suddenly altered physical conditions, namely, the

42S CONCLUSION. [Chap. XV.

mutual relation of organism to organism, — tlie improvement ol
one organism entailing the improvement or the extermination
of others ; it follows, that the amount of organic change in the
fossils of consecutive formations probahly serves as a fair measure
of the relative, though not actual lapse of time. A number of
species, however, keeping in a body might remain f:,r a long period
unchanged, whilst within the same period, several of these species^
by migrating into new countries and coming into competition with
foreign associates, might become modified; so that we must not
_ overrajie the accuracy oforggjii£j3bg^ngej,s r, mensurpi oiMmo^^^ yp

In the future I see open fields for far more important researches.
Psychology will be securely based on the foundation already-^ell
laid by Mr. Herbert Spencer, that of the necessary acquirement
of eacHroehtaT power and capacity by gradation. Much light will
be thrown on the origin of man and his history.

Authors of the highest eminence seem to be fully satisfied with
the view that each species has been independently created. To my
mindJt accords better with what we know of the laws impressed on
inatter by thejOregJjQC, that _the production and extinction of the
past and present inhabitants of the world, should have been due to
secondary causes, like those determining the birth and death of the |

^iividual. When I view all beings not as special creations, but
as the lineal descendants of some few beings which lived long before
the first bed of the Cambrian system was deposited, they seem to \
me to become ennobled. Judging from the past, we may safely
infer that not one living species will transmit its unaltered likeness
to a distant futurity. And of the species now living very few will
transmit progeny of any kind to a far distant futurity ; for the
manner in which all organic beings are grouped, shows that the
greater number of species in each genus, and all the species in
many genera, have left no descendants, but have become utterly
extinct. We can so far take a prophetic glance into futurity as to
foretell that it will be the common and widely-spread species,
belonging to the larger and dominant groups within each class,
which will ultimately prevail and procreate new and dominant
species. As all the living forms of life are the lineal descendants of
those which lived long before the Cambrian epoch, we may feel
certain that the ordinary succession by generation has never once
been broken, and that no cataclysm has desolated the whole world.
Hence we may look with some confidence to a secure future of
great length. And as natural selection works solely by and for the
good of each bein^, all corporeal and mental er.i-owments will tend
to progress towards perfectiou.

#'

Chap. XV.l CONCLUSION. 429 Jr" ^'

.>.

It IS interesting to contemplate a tangled bank, clothed with "i*
many plants of many kinds, with birds singing on the bushes, with ^
various msects flitting about, and with worms crawling throucrh^
the damp earth, and to reflect that these elaborately constructed U ,

forms, so diff-erent from each other, and dependent upon each other -^ ^ ^
m so complex,^manner, have all been produced by laws actincr - • . '"
aroundus^/ These laws, taken in the largest sense, being Growth 6 ^
withTieproduction ; Inheritance which is almost implied by repro- r^
duction; Variability from the indirect and direct action of the con-"^-^
ditions of life, and from use and disuse : a Ratio of Increase so high /'i
as to lead to a Struggle for Life, and as a consequence to Nahiral T ^
^^election, entailing Divergence of Character and the Extinction of ^ «J
less-improved forms. Thus, from the war of nature, from famine
and death, the most exalted object which we are capable of con-
ceivmg, namely, the production of the higher animals, directly
follows. There is grandeur in this view of life, with its several
powers, having been originally breathed by the Creator into a few
forms or into one ; and that, whilst this planet has gone cyclino- on
accordmg to the fixed law of gravity, from so simple a beginning
endless forms most beautiful and most wonderful have been and
are being evolved, j d. *

Glorrary

( «0 )

GLOSSARY

OP THE

PRINCIPAL SCIENTIFIC TEEMS USED IN THE
PRESENT VOLUME.*

Aberrant. — Foi*ms or gioxips of animals or plants which deviate in im-
portant characters from their nearest allies, so as not to be easily in-
cluded in the same group with them, are said to be aberrant. — ..«i«

Aberration (in Optics). — In the refraction of light by a convex lens the
rays passing through different parts of the lens are brought to a focus at
slightly different distances, — this is called spherical aberration ; at the
same time the coloured rays are separated by the prismatic action of
the lens and likewise brought to a focus at different distances, — this is
chromatic aberration.

Abnormal. — Contrary to the general rule.

Aborted. — An organ is said to be aborted, when its development has been
arrested at a very early stage.

Albinism. — Albinos are animals in which the usual colouring matters
characteristic of the species have not been produced in the skin and its
appendages. Albinism is the state of being an albino.

Alg^. — A class of plants including the ordinary sea-weeds and the fila-
mentous fresh-water weeds.

Alternation of Generations. — This term is applied to a peculiar mode
of reproduction which prevails among many of the lower animals, in
which the egg produces a living form quite different from its parent, but
from which the parent-form is reproduced by a process of budding, or
by the division of the substance of the first product of the egg.

Ammonites. — A group of fossil, spiral, chambered shells, allied to the
existing pearly Nautilus, but having the partitions between the cham-
bers waved in complicated patterns at their junction with the outer
wall of the shell.

Analogy. — That resemblance of structures which depends upon simi-
laiity of function, as in the wings of insects and birds. Such structures
are said to be analogous^ and to be analogues of each other.

• I am indebted to the kindness of Mr. W. S. Dallas for this Glossary, which has been
given because several readers have complained to me that some of the terms used were
uaintelligible to them. Mr. Dallas has endeavoured to give the explanations of tbe
ienus in as poj-ular a form as possible.

GLOSSAKV. 431

Animaix^ULE. — A minute animal : generally applied to those visible only by
the microscope.

Annelids. — A class of worms in which the surface of the body exhibits a
more or less distinct division into rings or segments, generally provided
with appendages for locomotion and with gills. It includes the ordinary
marine woi-ms, the earthworms, and the leeches.

Antenna. — Jointed organs appended to the head in Insects, Crustacea and
Centipedes, and not belonging to the mouth.

Anthers. — The summits of the stamens of flowers, in which the pollen or
fertilising dust is produced.

Aplacentalia, Aplacentata or Aplacental Mammals. See Mammalia.

Archetypal. — Of or belonging to the Archetype, or ideal primitive form
upon which all the beings of a group seem to be organised.

Articulata. — A great division of the Animal Kingdom characterised gene-
rally by having the surface of the body divided into rings, called seg-
ments, a greater or less number of which are furnished with jointed legs
(such as Insects, Crustaceans and Centipedes).

Asymmetrical. — Having the two sides unlike.

Atrophied. — Arrested in development at a very early stage.

Balanus. — The genus including the common Acorn-shells which live in
abundance on the rocks of the sea-coast.

Batrachians. — A class of animals allied to the Reptiles, but undergoing
a peculiar metamorphosis, in which the young animal is generally
aquatic and breathes by gills. (Examples, Frogs, Toads, and Newts.)

Boulders. — Large transported blocks of stone generally imbedded in clays
or gravels.

Brachiopoda. — A class of marine MoUusca, or soft-bodied animals, fur-
nished with a bivalve shell, attached to submarine objects by a stalk
which passes through an aperture in one of the valves, and furnished
with fringed arms, by the action of which food is carried to the
mouth.

Branchi^. — Gills or organs for respiration in water.

Branchial. — Pertaining to gills or branchiae.

Cambrian System. — A Series of very ancient Palaeozoic rocks, between the
Laurentian and the Silurian. Until recently these were regarded as
the oldest fossiliferous rocks.

Canid^. — The Dog-family, including the Dog, Wolf, Fox, Jackal, &c.

Carapace. — ^The shell enveloping the anterior part of the body in Crusta-
ceans generally ; applied also to the hard shelly pieces of the Cirripedes.

Carboniferous. — This terra is applied to the great formation which
includes, among othsr rocks, the coal-measures. It belongs to the
oldest, or Palaeozoic, system of formations.

Caudal. — ^Of or belonging to the tail.

Cephalopods. — The highest class of the Mollusca, or soft-bodied animals,
characterised by having the mouth surrounded by a greater or less
number of fleshy arms or tentacles, which, in most living species, are
furnished with sucking-cups. {Examples, Cuttle-fish, Nautilus.)

Cetacea, — An order of Mammalia, including the Whales, Dolphins, &c.,

432 GLOSSARY.

^y

having the form of the body fish-like, the akin naked, and only the fore-
limbs developed.

Chelonia, — An order of Reptiles including the Turtles, Tortoises, &c.

CiRRiPEDES. — An order of Crustaceans including the Barnacles and Acorn-
shells. Their young resemble those of many other Crustaceans in form ;
but when mature they are always attached to other objects, eithei
directly or by means of a stalk, and their bodies are enclosed by a
calcareous shell composed of several pieces, two of which can open to
give issue to a bunch of curled, jointed tentacles, which represent the
limbs.

Coccus. — The genus of Insects including the Cochineal. In these the male
is a minute, winged fly, and the female generally a motionless, berry-
like mass.

Cocoon. — A case usually of silky material, in which insects are frequently
enveloped during the second or resting-stage (pupa) of their existence.
The term " cocoon-stage " is here used as equivalent to '' pupa-stage."

C(EIX)SPERM0US. — A term applied to those fruits of the Umbelliferse
which have the seed hollowed on the inner face.

COLEOPTERA. — Beetles, an order of Insects, having a biting mouth and the
first pair of wings more or less horny, forming sheaths for the second
pair, aud usually meeting in a straight line down the middle of the
back.

Column. — A peculiar organ in the flowers of Orchids, in which the stamens,
style and stigma (or the reproductive parts) are united.

Composite or Compositous Plants. — Plants in which the inflorescence
consists of numerous small flowers (florets) brought together into a
dense head, the base of which is enclosed by a common envelope.
(^Examples, the Daisy, Dandelion, &c.)

Conferva. — The filamentous weeds of fresh water.

Conglomerate. — A rock made up of fragments of rock or pebbles,

cemented together by some other material.
Corolla. — The second envelope of a flower usually composed of coloured,

leaf-like organs (petals), which may be united by their edges either in

the basal part or throughout.
Correlation. — The normal coincidence of one phenomenon, character, &c.;

with another.
Corymb. — A bunch of flowers in which those springing from the lower

part of the flower stalk are supported on long stalks so as to be nearly

on a level with the upper ones.
Cotyledons. — The first or seed-leaves of plants.

Crustaceans. — A class of articulated animals, having the sicin of the body
generally more or less hardened by the deposition of calcareous matter,
breathing by means of gills. (^Examples, Crab, Lobster, Shrimp, &c.)

CuRCULiO. — The old generic term for the Beetles known as Weevils, cha-
racterised by their four-jointed feet, and by the head being produced
into a sort cf beak, upon the sides of which the antennae are inserted.

Cutaneous. — Of or belonging to the skin.

Degradation. — The wearing down of land by the action of the sea or of
meteoric agencies.

GLOSSARY. 433

Denudation. — The wearing away of the surface of the land by water.

Devonian System or formation. — A series of Palaeozoic rocks, including
the Old Red Sandstone.

Dicotyledons or Dicotyledonous Plants. — A class of plants character-
ised by having two seed-leaves, by the formation of new wood between
the bark and the old wood (exogenous growth) and by the reticulation
of the veins of the leaves. The parts of the flowers are generally in
multiples of five.

Differentiation, — The separation or discrimination of parts or organs
which in simpler forms of life are more or less united.

Dimorphic. — Having two distinct forms. — Dimorphism is the condition of \^
the appearance of the same species under two dissimilar forms. •^

DiCECiOUS. — Having the organs of the sexes upon distinct individuals.

DiORiTE. — A peculiar form of Greenstone.

Dorsal. — Of or belonging to the back.

Edentata. — A peculiar order of Quadrupeds, characterised by the absence
of at least the middle incisor (front) teeth in both jaws. (^Examples^
the Sloths and Armadillos.)

Elytra. — The hardened fore-wings of Beetles, serving as sheaths for the
membranous hind-wings, which constitute the true organs of flight.

Embryo. — The young animal undergomg development within the egg oi
womb.

Embryology. — The study of the development of the embryo.

Endemic. — Peculiar to a given locality.

Entomostraca. — A division of the class Crustacea, having all the seg-
ments of the body usually distinct, gills attached to the feet or organs
of the mouth, and the feet fringed with fine hairs. They are generally
of small size.

Eocene. — The earliest of the three divisions of the Tertiary epoch of geolo-
gists. Rocks of this age contain a small proportion of shells identical
with species now living.

Ephemerous Insects. — Insects allied to the May-fly.

Fauna. — The totality of the animals naturally inhabiting a certain
country or region, or which have lived during a given geological
period.

Felid^. — The Cat-family.

Feral. — Having become wild from a state of cultivation or domestication.

Flora. — The totality of the plants growing naturally in a country, or
during a given geological period.

Florets. — Flowers imperfectly developed in some respects, and collected
into a dense spike or head, as in the Grasses, the Dandelion, &c.

FcETAL. — Of or belonging to the foetus, or embyro in course of develop-
ment.

Foraminifera. — A class of animals of very low organisation, and generally
of small size, having a jelly-like body, from the surface of which deli-
cate filaments can be given off and retracted for the prehension of
external objects, and having a calcareous or sandy shell, usually
divided into chambers^ and perforated with small apertures.
ft 2 F

^'

V

434 GLOSSARY.

FjasiLiFEiious. — Containing fossils.

FossoiUAL.~naving a faculty of digging. The Fossorial Hfrnenoptera are

a group of Wasp-like Insects, which burrow in sandy soil to make nests

for their young.
Frenum (pi. Frena). — A small band or fold of skin.
FuXGi (sing. Fungus).— A class of cellular plants, of which Mushrooms,

Toadstools, and Moulds, are familiar examples.
FCRCULA. The forked bone formed by the union of the collar-bones in many

birds, such as the common Fowl.

Gallinaceous Birds.— An order of Birds of which the common Fowl,
Turkey, and Pheasant, are well-known examples.

Gallus. The genus of birds which includes the common Fowl.

Ganglion.— A swelling or knot from which nerves are given off as from a

centre.
Ganoid Fishes. — Fishes covered with peculiar enamelled bony scales

Most of them are extinct.
Germinal Vesicle.— A minute vesicle in the eggs of animals, from which

the development of the embyro proceeds.
Glacial Period.— A period of great cold and of enormous extension of
ice upon the surface of the earth. It is believed that glacial periods
have occurred repeatedly during the geological history of the earth, but
the term is generally applied to the close of the Tertiary epoch, when
nearly the whole of Europe was subjected to an arctic climate.
3land.— An organ which secretes or separates some peculiar product from
the blood or sap of animals or plants.

CiLOTTiS. The opening of the windpipe into the oesophagus or gullet.

Gneiss.- A rock approaching granite in composition, but more or less
^ lam'inated, and really produced by the alteration of a sedimentary
deposit after its consolidation.
Grallatores.— The so-called Wading-birds (Storks, Cranes, Snipes, &c.),
which are generally furnished with long legs, bare of feathers above
the heel, and have no membranes between the toes.
Granite.— A rock consisting essentially of crystals of felspar and mica in
a mass of quartz.

Habitat.— The locality in which a plant or animal naturally lives.
HemipterA.— An order or sub-order of Insects, characterised by the posses-
sion of a jointed beak or rostrum, and by having the fore-wings horny
in the basal portion and membranous at the extremity, where they cross
^ each other. This group includes the various species of Bugs.
ft /"^ Hermaphrodite. — Possessing the organs of both sexes.

/ Homology.— That relation between parts which results from their deve-
\/ lopment from corresponding embryonic parts, either in different animals,

^ as in the case of the arm of man, the fore-leg of a quadruped, and the

wincr of a bird ; or in the same individual, as in the case of the fore and
hind legs in quadrupeds, and the segments or rings and their append
dages of which the body of a worm, a centipede, &c., is composed. Tn(
latter is called serial homology. The parts which stand in such a relatiot
to each other are said to be homologous^ and one such part or organ i

GLOSSARY. 435

called the homologue of the other. In different plants the parts of the

flower are homologous, and in general these parts are regarded aa

homologous with leaves.
HOMOPTERA. — An order or sub-order of Insects having (like the Ilemi-

ptera) a jointed beak, but in which the fore-wings are either wholly

membranous or wholly leathery. The Cicadse, Frog-hoppers, and

AphideSj are well-known examples.
Hybrid. — The offspring of the union of two distinct species.
HoiENOPTERA. — An order of Insects possessing biting jaws and usually

four membranous wings in which there are a few veins. Bees and

Wasps are familiar examples of this group.
Hypertrophied. — Excessively developed. L'""^^^^

ICHNEUMONID^. — A family of Hymenopterous insects, the members of
which lay their eggs in the bodies or eggs of other insects.

Imago. — The perfect (generally winged) reproductive state of an insect.

Indigens. — 1 The aboriginal animal or vegetable inhabitants of a country
or region.

Inflorescence. — The mode of arrangement of the flowers of plants.

Infusoria. — A class of microscopic Animalcules, so called from their
having originally been observed in infusions of vegetable mattei's. They
consist of a gelatinous material enclosed in a delicate membrane, the
whole or part of which is furnished with short vibrating hairs (called
cilia), by means of which the animalcules swim through the water or
convey the minute particles of their food to the orifice of the mouth. ;

Insectivorous. — Feeding on Insects, i

Invertebrata, or Invertebrate Animals. — Those animals which do not
possess a backbone or spinal column.

Lacuna. — Spaces left among the tissues in some ot the lower animals,
and serving in place of vessels for the circulation of the fluids of the body.

Lamellated. — Furnished with lamellae or little plates.

Larva (pi. Larv^). — The first condition of an insect at its issuing from the
egg, when it is usually in the form of a grub, caterpillar, or maggot.

Larynx. — The upper part of the windpipe opening into the gullet.

Laurentian. — A group of greatly altered and very ancient rocks, which
is greatly developed along the course of the St. Lawrence, whence the
name. It is in these that the earliest known traces of organic bodies
have been found.

Leguminos^. — An order of plants represented by the common Peas and
Beans, having an irregular flower in which one petal stands up like a
wing, and the stamens and pistil are enclosed in a sheath formed by two
other petals. The fruit is a pod (or legume).
i: Lemuridje. — A group of four-handed animals, distinct from the Monkeys
|, and approaching the Insectivorous Quadrupeds in some of their charac-
ters and habits. Its members have the nostrils curved or twisted, and
a claw instead of a nail upon the first fiuger of the hind hands.

Lepidoptera. — An order of Insects, characterised by the possession of a
spiral proboscis, and of four large more or less scaly wings. If, includes
the well-knsjwu Butterflies and Moths.

2 P 2

436 GLOSSARY.

V

1/

\/

Littoral. — luhabitiug the seashore.

Loess.— A marly deposit of recent (Post-Tertiary) date, which occupies a
great part of the valley of the Rhine, N v^ "^ ''

Malacostraca.— The higher division of the Ciustacea, including the
ordinary Crabs, Lobsters, Shrimps, &c., together with the Woodlice and
Sand-hoppers.
Mammalia.— The highest class of animals, including the orCinary hairy
quadrupeds, the Wnales, and Man, and characterised by the production
of living younsr which are nourished after birth by milk from the
teats {Ma7nmx, Mammary glands) of the mother. A st. 'king difference
' in embryomc development has led to the division of this -lass into two
great groups ; in one of these, when the embryo has attained a certain
stage, a vascular connection, called the placenta, is formed between the
embryo and the mother ; in the other this is wanting, and the young
are produced in a very incomplete state. The former, including the
greater part of the class, are called Placental mammals ; the latter, or
Aplacental mammals, include the Marsupials and Monotremes (^Orni-
thorhynchus).
lilAMMiFEROUS. — Having mammae or teats (see Mammalia).
Mandibles, in Insects.— The first or uppermost pair of jaws, which are
generally solid, horny, biting organs. In Birds the term is applied to
both jaws with their horny coverings. In Quadrupeds the mandible
is properly the lower jaw.
Marsupials.— An order of Mammalia in which the young are born in a
very incomplete state of development, and carried by the mother, while
sucking, in a ventral pouch (marsupium), such as the Kangaroos,
Opossums, &c. (see Mammalia).
Maxillae, in Insects.— The second or lower pair of jaws, which are com-
posed of several joints and furnished with peculiar jointed appendages
called palpi, or feelers.
Melanism.— The opposite of albinism ; an undue development of colouring

material in the skin and its appendages.
Metamorphic Rocks.— Sedimentary rocks which have undergone altera-
tion, generally by the action of heat, subsequently to their deposition
aud consolidation.
Mollusca.— One of the great divisions of the Animal Kingdom, including
those animals which have a soft body, usually furnished with a sheh,
and in which the nervous ganglia, or centres, present no definite general
arrangement. They are generally known under the denomination of
" shell-fish ;" the cuttle-fish, and the common snails, whelks, oysters,
mussels, and cockles, may serve as examples of them.
Monocotyledons, or Monocotyledonous plants.— Plants in which the
seed sends up only a single seed-leaf (or cotyledon) ; characterised by
the absence of consecutive layers of wood in the stem (endogenous
growth), by the veins of the leaves being generally straight, and by the
parts of the flowers being generally in multiples of three. {Examples^
Grasses, Lilies, Orchids, Palms, &c.)
Moraines.— The accumulations of fragments of rock brought down by

glaciers.
Morphology.— The law of form or structure independent of function.

GLOSSARY. 437

Mysis-stage. — A stage in the development of certain Crvrsta leanx
(Prawns), in which they closely resemble the adults of a genus (ifysM^
belonging to a slightly lower group.

Nascent. — Commeucmg development.

Natatory. — Adapted for the purpose of swimming.

N'auplius-form. — ^The earliest stage in the development of many Crustacea,
especially belonging to the lower groups. In this stage the animal has
a slior; body, with indistinct indications of a division into segments
and three pairs of fringed limbs. This form of the common fresh-water
Cyclops was described as a distinct genus under the name of NaupUus.

Neuration. — The arrangement of the veins or nervures in the wings of
Insects.

Neuters. — Imperfectly developed females of certam social msects (sucn as
Ants and Bees), which perform all the labours of the community.
Honce they are also called workers.

Nictitating Membrane. — A semi-transparent membrane, which can be
drawn across the eye in Birds and Reptiles, either to moderate the
effects of a strong light or to sweep particles of dust, &c., from the sur-
face of the eye.

Ocelli. — The simple eyes or stemmata of Insects, usually situated on the

crown of the head between the great compound eyes.
(Esophagus. — The gullet.

Oolitic. — A great series of secondary rocks, so called from the texture of
some of its members, which appear to be made up of a mass of small
egg-like calcareous bodies.

Operculum. — A calcareous plate employed by many Mollusca to close the
aperture of their shell. The opercular valves of Cirripedes are those
which close the aperture of the shell.

OuBiT. — The bony cavity for the reception of the eye.

Organism. — An organised being, whether plant or animal.

Orthospermous. — A term applied to those fruits of the Umbellifer»
which have the seed straight.

Osculant. — Forms or groups apparently intermediate between and con-
necting other gi'oups are said to be osculant.

Ova. — Eggs.

Ovarium or Ovary (in plants).— The lower part of the pistil or femaio
organ of the flower, containing the ovules or incipient seeds ; by growtb
after the other organs of the flower have fallen, it usually becomes
converted into the fruit.

'^TOvigerous. — Egg-bearing.

Ovules (of plants). — ^The seeds in the earliest condition.

HpACHYDERMS. — A group of Mammalia, so called from their thick skinSj

and including the Elephant, Rhinoceros, Hippopotamus, &c.
Paleozoic. — The eldest system of fossiliferous rocks.

Palpi. — Jointed appendages to some -^f the organs of the mouth in Insectf
and Crxistacca

*38 GLOSSARY.

^

l^

1/

V

Papilionace^. — ^An order of Plants (see Leguminosje).— The flowers of
these plants are called papilionaceous, or butterfly-like, from the
fancied resemblance of the expanded superior petals to the wings fo a
butterfly.

Parasite. — An animal or plant livmg upon or in, and at the expense of,
another organism.

Parthenogenesis. — The production of living organisms from unimpreg-

nated eggs or seeds.
Pedunculated. — Supported upon a stem or stalk. The pedunculated oak

has its acorns borne upon a footstalk.

Peloria or Pelorism. — The appearance of regularity of structure in the
flowers of plants which normally bear irregular flowers.

Pelvis. — The bony arch to which the hind limbs of vertebrate animals are
articulated.

Petals. — ^The leaves of the corolla, or second circle of organs in a flower.
They are usually of delicate texture and brightly coloured.

Phyllodineous. — Having flattened, leaf-like twigs or leafstalks instead of

true leaves.
Pigment. — The coiouring material produced generally m the superficial

parts of animals. The cells secreting it are called pigment-cells.

Pinnate. — Bearing leaflets on each side of a central stalk.

Pistils. — The female organs of a flower, which occupy a position in th*
centre of the other floral organs. The pistil is generally divisible into
the ovary or germen, the style and the stigma.

Placentalia, Placentata, or Placental Mammals. — See Mammalia.
Plantigrades. — Quadrupeds which walk upon the whole sole of the foot,

like the Bears.
Plastic. — Readily capable of change.
Pleistocene Period. — The latest portion of the Tertiary epoch.

Plumule (in plants). — The minute bud between the seed-leaves of newly-
germinated plants.

Plutonic Rocks. — Rocks supposed to have been produced by igneous action
in the depths of the earth.

Pollen. — The male element in flowering plants ; usually a fine dust pro-
duced by the anthers, which, by contact with the stigma effects the
fecundation of the seeds. This impregnation is brought about by means
of tubes (jpollen-tuhes) which issue from the pollen-grains adhering to
the stigma, and penetrate through the tissues until they reach the
ovary.

POLYANDROUS (flowers). — Flowers having many stamens.

Polygamous Plants. — Plants in which some flowers are unisexual and
others hermaphrodite. The unisexual (male and female) flowers, may be
on the same or on diflferent plants.

Polymorphic. — Presenting many forms.

POLYZOARY. — The common structure formed by the cells of the Polyzoa,
such ?,K the v/ell-known Sea-mats.

Prehensile. — Capable of grasping.
Prei'OTEnt — Having a superiority of power,

GLOSSAHY. 433

Primaries. — ^The feathers forming, the tip of the wing of a bird, aid in-
serted upon that part which rej)resents the hand of man.

Processes. — Projecting portions of bones, Usually for the attachment of
muscles, ligaments, &c.

Fkopolis. — A resinous material collected by the Hive-Bees from the
opening buds of various trees.

Protean. — Exceedingly variable.

Protozoa. — The lowest great division of the Animal Kmgdom. Thesi*
animals are composed of a gelatinous material, and show scarcely any
trace of distinct organs. The Infusoria, Foraminifera, and Sponges,
with some other forms, belong to this division.

Pupa (pi. Pup^). — ^The second stage in the development of an Insect, from
which it emerges in the perfect (winged) reproductive form. In most
insects the pupal stage is passed in perfect repose. The chrysalis is the
pupal state of Butterflies.

Radicle. — ^The minute root of an embryo plant.

Hamus. — One half of the lower jaw in the Mammalia. The portion which
rises to articulate with the skull is called the ascending ramus.

Ra:noe. — The extent of country over which a plant or animal is naturally
spread. Range in time expresses the distribution of a species or group
through the fossiliferous beds of the earth's crust.

Hetina. — The delicate inner coat of the eye, formed by nervous filaments
spreading from the optn nerve, and serving for the perception of the
impressions produced by light.

Retrogression. — Backward development. "When an animal, as it ap-
proaches maturity, becomes less perfectly organised than might be
expected from its early stages and known relationships, it is said to
undergo a retrograde development or metamorphosis.

Rhizopods. — A class of lowly organised animals (Protozoa), having a gela-
tinous body, the surface of which can be protruded in the form of root-
like processes or filaments, which serve for locomotion and the prehen-
sion of food. The most important order is that of the Foraminifera.

Rodents. — The gnawing Mammalia, such as the Rats, Rabbits, and
Squirrels. They are especially characterised by the possession of a
single pair of chisel-like cutting teeth in each jaw, between which and
the grinding teeth there is a great gap.

KUBUS. — The Bramble Genus.

Rudimentary. — Very imperfectly developed.

Ruminants. — The group of Quadrupeds which ruminate or chew the
cud, such as oxen, sheep, and deer. They have divided hoofs, and are
destitute of front teeth in the upper jaw.

Sacral. — Belonging to the sacrum, or the bone composed usually of two

or more united vertebrae to which the sides of the pelvis in vertebrate

animals are attached.
Sarcode. — ^The gelatinous material of which the bodies of the lowest

animals (Protozoa) are composed.
Scutell^e. — The horny plates with v/hich the feet of birds are generally

inore or less covered, especially in front.
Sedimentary Formations. — Rocks deposited as sediments from water.

440 GLOSSARY

1/

V

Segments. — The transverse rings of which the body of an articulate
animal or Annelid is composed.

Sepals. — The leaves or segments of the calyx, or outermost envelope Df
an ordinary flower. They are usually green, but sometimes brightly
coloured.

Serratures. — Teeth like those of a saw.

.Sessile. — Not supported on a stem or footstalk.

Silurian System. — A very ancient system of fossiliferous rocks oeiougjng
to the earlier part of the Falaozoic series.

Specialisation. — The setting apart of a particular organ for the perform-
ance of a particular function.

Spinal Chord. — The central portion of the nervous system in the Verte-
brata, whici descends from the brain through the arches of the ver-
tebra, and gives oft" nearly all the nerves to the various organs of the
body.

Stamens. — ^The male organs of flowering plants, standing in a circle within
the petals. They usually consist of a filament and an anther, the
anther being the essential part in which the pollen, or fecundating
dust, is formed.

Sternum. — The breast-bone.

Stigma. — The apical portion of the pistil in flowering plants.

Stipules. — Small leafy organs placed at the base of the footstalks of the
leaves in many plants.

Style. — The middle portion of the perfect justil, which rises like a cclumn
from the ovary and supports the stigma at its summit.

Subcutaneous. — Situated beneath the skin.

Suctorial. — ^Adapted for sucking.

Sutures (in the skull). — The lines of ;unction of the bones of which the
skull is composed.

Tarsus (pi. Tarsi). — The jointed feet of articulate animals, such as Insects^

Teleostean Fishes. — Fishes of the kind familiar to us in the present day,
having the skeleton usually completely ossified and the scales horny.

Tentacula or Tentacles. — Delicate fleshy organs of prehension or touch
possessed by many of the lower animals.

Tertiary, — The latest geological epoch, immediately preceding the esta-
blishment of the present order of things.

Trachea. — The wind-pipe or passage for the admission of air to the lungs.

Iridactyle. — Three-fingered, or composed of three movable parts attached
to a common base.

Trilobites. — A peculiar group of extinct Cnistaceanj, somewhat resembling
the Woodlice in external form, and, like some of them, capable of rolling
themselves up into a ball. Their remains are found only in the Palaeo-
zoic rocks, and most abundantly in those of Silurian age.

Trimorphic. — Presenting three distinct forms.

Umbelliper^. — ^An order of plants in which the flowers, which contain
five stamens and a pistil with two styles, are supported upon footstalks
which spring from the top of the flower stem and spread out like the
wires of an umbrella, so as to bring all the flowers in the same head
(umbel) nearly to the same level. (Examples, Parsley and Carrot.)

GLOSSAKl. 441

Ungulata. — Hoofed quadrupeds.
Unicellular. — Consisting of a single cell.

Vascular. — Containing blood-vessels.

Vermiform. — Like a woi*m.

Vertebrata: or Vertebrate Animai^. — The highest division of the
animal kingdom, so called from the presence in most cases of a back-
bone composed of numerous joints or vertehrgs, which constitutes the
centre of the skeleton and at the same time supports and protects
the central parts of the nervous system.

Whorls. — The cii'cles or spiral lines in which the parts of plants are

arranged upon the axis of growth.
Workers. — See Neuters.

ZoisA-STAGE. — ^The earliest stage m the development of many of the higher
Crustacea, so called from the name of Zoea applied to these young
animals when they were supposed to constitute a peculiar genus.

ZooiDS. — In many of the lower animals (such as the Corals, Medusa, &c.)
reproduction takes place in two ways, namely, by means of eggs and
by a process of budding with or without separation from the parent of
the product of the latter, which is often very different from that of the
€gg. The individuality of the species is represented by the whole of
tha form produced between two sexual reproductions; and these formai
which are apparently individual animals, have been called zooids*

l^

( 443 )

INDEX.

ABEREAKT.

A.

Aberrant groups, 379.

Abyssinia, plants of, 340.

Acclimatisation, 112.

Adoxa, 173.

Allinities of extinct species, 301,.

of organic beings, 378.

Agassiz, on Amblyopsis, 112.

, on groups of specici suddenly

appearing, 289.

■ , on prophetic formfj, 301.

, on embryologifxtl succession,

310.

, on the Glacial period, 330.

, on embryological characters,

368.

, on the latest tertiary forms, 278.

. , on parallelism of embryological

development and geological suc-
cession, 396.
-, Alex., on pedicellariae, 191.

Algae of New Zealand, 338.
Alligators, males, fighting, 69.
Alternate generations, 387.
Amblyopsis, blind fish, 112.
America, North, productions allied to

those of Europe, 333.
, , boulders and glaciers of,

335.
, South, no modern formations

on west coast, 272.
Ammonites, sudden extinction of, 297.
Anagallis, sterility of, 236.
Analogy of variations, 127.
Ancylus, 345.
Andaman Islands inhabited by a toad,

350.
Animals, not domesticated from being

variable, 13.
, domestic, descended from seve-
ral stocks, 14.

, , acclimatisation of, 112.

■ • of Australia, 90.

with thicker fur in cold climates,

107.

BAEB.

Animals, blind, in caves, 110.
■ ■ , extinct, of Australia, 310.
Anomma, 222.
Antarctic islands, ancient ficra

355.
Antechinus, 373.
Ants attending aphides, 207.

, slave-making instinct, 217.

neuters, structure of, 230,

o£

iial

Apes, not having acquired intelle-

powers, 181.
Aphides, attended by ants, 207.
Aphis, development of, 390.
Apteryx, 140.
Arab horses, 26.
Aralo-Caspian Sea, 311.
Archeopteryx, 284.
Archiac, M. de, on the succession of

species, 299.
Artichoke, Jerusalem, 114,
Ascension, plants of, 347.
Asclepias, pollen of, 151.
Asparagus, 325.
Aspicarpa, 367.
Asses, striped, 127.

, improved by selection, 30.

Ateuchus, 109.

Aucapitaine, on land-shells, 353.

Audubon, on habits of frigate-bii^l,

142.

variation in birds' nests,

on

208.

on heron eatinEr seeds, 346.

Australia, animals of, 90.

, dogs of, 211.

, extinct animals of, 310.

, European plants in, 337.

, glaciers of, 335.

Azara, on flies destroying cattle, 56.
Azores, flora of, 328.

B.

Babiugton, Mr., on British plants, 37
Bacr, Von, standard of Highness, 97.

, comparison of bee and fish

308.

444

6AER.

IJS DEX.

CATTir.

Baer, Von, embryonic similarity of

the Vertebrata, 387.
Baker, Sir S., on the giraffe, 178.
Balancement of growth, 117.
Baleen, 182.
Barberry, flowers of, 77.
Barrande, M., on Silurian colonies,

291.
— — , on the succession of species,

299.
, on parallelism of palaeozoic

formations, 301.
, on affinities of ancient

species,

302.

Barriers, importance of, 317.
Bates, Mr., on mimetic butterflies,

375,376.
Batrachians on islands, 350.
Bats, how structure acquired, 140.

, distribution of, 351.

Bear, catching water-insects, 141,
Beauty, how acquired, 159, 414.
Bee, sting of, 163.

, queen, killing rivals, 164.

y Australian, extermination

of,

59.

Bees fertilising flowers, 57.

, hive, not sucking the red clover,

75.

, Ligurian, 75.

, hive, cell-making instinct, 220.

, variation in habits, 208.

, parasitic, 216.

, humble, cells of, 220.

Beetles, wingless, in Madeira, 109.

with deficient tarsi, 109.

Bentham, Mr., on British plants, 37.

, on classification, 369.

Berkeley, Mr., on seeds in salt water,
324.

Bermuda, birds of, 348.

Birds acquiring fear, 208,

, beauty of, 161.

annually cross the Atlantic, 329.

, colour of, on contineaLs, 107.

, footsteps, and remains of, in

secondary rocks, 284.

, fossil, in caves of Brazil, 310.

, of Madeira, Bermuda, and Ga-
lapagos, 348, 349.

, song of males, 70.

transporting seeds, 328.

, waders, 345.

, wingle.ss, 108, 140.

Bizcacha, 318.

, affinities of, 379.

Bladder for swimming, in fish, 147.
Blindness of cave animals, 110.
Blyth, Mr., on distinctness of Indian

cattle, 14.

f on striped hemionus, 128.

-, on crossed geese, 240.

Borrow, Mr., on the Spanish pointer,

26.
Bory St.Vincent, on Batrachians, 350.
Bosquet, M., on fossil Chthamalus,

284.
Boulders, erratic, ou the Azores, 328,
Branchia?, 148, 149.

of crustaceans, 152.

Braun, Prof., on the seeds of Fuina-

riace£e, 174.
Brent, Mr., on house-tumblers, 210.
Britain, mammais of, 352.
Broca, Prof, on Natural Selection,

170.
Bronn, Prof, on duration of specific

forms, 275.

, various objections by, 170.

Brown, Robert, on classification, 366.
— — , Se'quard, on inherited mutila-
tions, 108.
Busk, Mr., on the Polyzoa, 193.
Butterflies, mimetic, 375, 376.
Buzareingues, on sterility of varieties,

258.

C.

Cabbage, varieties of, crossed, 78.

Calceolaria, 239.

Canary-birds, sterility of hybrids,

240.
Cape de Verde islands, productions of,

354.

, plants of, on mountains, 337.

Cape of Good Hope, plants of, 101,

347.
Carpenter, Dr., on foraminifera, 308.
Carthamus, 173.
Catasetum, 155, 372.
Cats, with blue eyes, deaf, ?,

, variation in habits of, 209.

curling tail when going tc

spring, 162.
Cattle destrcying fir-trees, 56.
destroyed by flies in Par-3g'.ja?

56.

CATTLE.

INDEX.

CCVIER.

445

Cattle, breeds of, locally extinct, 86.
, fevtility of Indian and European

breeds, 241.

, Indian, 14, 241.

Cave, inhabitants of, blind, 110.
Cecidomyia, 387.

Celts, proving antiquity of man, 13.
Centres of creation, 320.
Cephalopoda, structure of eyes, 151.

, development of, 390.

Cercopithecus, tail of, 189.

Ceroxylus laceratus, 182.

Cervulus, 240.

Cetacea, teeth and hair, 115.

. , development of the whalebone,

182.
Cetaceans, 182.
Ceylon, plants of, 338.
Chalk formation, 297.
Characters, divergence of, 86.

, sexual, variable, 119, 123.

, adaptive or analogical, 373.

Charlock, 59.

Checks to increase, 53.

, mutual, 55.

Chelae of Crustaceans, 193.
Chickens, instinctive tameness of, 211.
Chironomus, its asexual reproduction,

387.
Chthamalinse, 271.
Chthamalus, cretacean species of, 284.
Circumstances favourable to selection

of domestic producta, 29.

to natural selection, 80.

Cirripedes capable of crossing, 79.

, carapace aborted, 118.

, their ovigerous frena, 148.

, fossil, 284.

, larvae of, 389.

ClaparMe, Prof, on the hair-claspers

of the Acaridse, 153.
Clarke, Rev. W. B., on old glaciers in

Australia, 335.
Classification, 363.
Clift, Mr., on the succession of types,

310.
Climate, effects of, in checking in-
crease of beings, 54.
■ , adaptation of, to organisma,

112.
Climbing plants, 147.

, development of, 196.

Clover visited oy bees, 75,
Cobites, intestine of, 147.

Cockroach, 59.

Collections, palaeontological, poor,
270.

Colour, influenced by climate, 107.

, in relation to attacks by flies,

159.

Columba livia, parent of domestic
pigeons, 17.

Colymbetes, 345.

Compensation of growth, 117.

Compositae, flowers and seeds of, 116,

■ , outer and inner florets of, 173,

, male flowers of, 398.

Conclusion, general, 421.

Conditions, slight changes in, favour-
able to fertility, 251.

Convergence of genera, 100.

Coot, 142.

Cope, Prof., on the acceleration or
retardation of the period of repro-
duction, 149.

Coral-islands, seeds drifted to, 326.

reefs, indicating movements of

earth, 326.

Corn-crake, 143.

Correlated variation in domestic pro-
ductions, 9.

Coryanthes, 154.

Creation, single centres of, 320.

Crinum, 238.

Croll, Mr., on subaenal denudation,
267, 269.

, on the age of our oldest form-
ations, 286.

on alternate Glacial periods in

the North and South, 336.

Crosses, reciprocal, 244.

Crossing of domestic animals, import-
ance in altering breeds, 15.

, advantages of, 76, 77.

, unfavourable to selection, 80,

Criiger, Dr., on Coryanthes, 154.

Crustacea of New Zealand, 338.

Crustacean, blind, 110.

air-breathers, 152.

Crustaceans, their chela?, 193.

Cryptocerus, 231.

Ctenomys, blind, 110.

Cuckoo, instinct of, 205, 212.

Cunningham, Mr., on the flight of
the logger-headed duck, 108.

Currants, grafts of, 246.

Currents of sea, rate of, 325.

Cuvier,on conditions of existence, 205

4^6

CCVIER.

INDEX.

EXTINCTION.

Cuvier, on fossil monkeys, 283, 284.

, Fred., on instinct, 205.

Cyclostoma, resisting salt water, 353,

D.

Dana, Prof., on blind cave-animals, 111.

— — , on relations of crustaceans of
Japan, 334.

, on crustaceans of New Zea-
land, 338.

Dawson, Dr., on eozoon, 287.

De Candolle, Aug. Pyr., on struggle
for existence, 49.

, on umbelliferse, 116.

, on general affinities, 379.

De Candolle, Alph., on the variability
of oaks, 40.

■ -, on low plants, widely dispersed,

359.

, on widely-ranging plants being

variable, 43.

, on naturalisation, 89.

, on winged seeds, 117.

, on Alpine species suddenly be-
coming rare, 135.

, on distribution of plants with

large seeds, 326.

, on vegetation of Australia, 340.

, on fresh-water plants, 345.

, on insular plants, 347.

Degradation of rocks, 266.

Denudation, rate of, 268.

of oldest rocks, 287.

of granitic areas, 274.

Development of ancient forms, 307.

Devonian system, 305.

Dianthus, fertility of crosses, 243.

Dimorphism in plants, 35, 252.

Dirt on feet of birds, 328.

Dispersal, means of, 323.

during Glacial period, 330.

Distributioiv^ geographical, 316.

, means of, 323.

Disuse, effects of, under nature, 108.

Divergence of character, 86.

Diversification of means for same
general purpose, 153.

Division, physiological, of labour, 89.

Dog, resemblance of jaw to that of
the Thylacinus, 374.

Dogs, hairless, with imperfect teeth, 9.

descended from several wild

stocks, 15.

, doraestJA instincts of, 210.

Dogs, inherited civilisation of, 210.

, fertility of breeds together, 241.

, of crosses, 256.

-, proportions of body in different

breeds, when young, 392.

Domestication, variation under, 5.

Double flowers, 230.

Downing, Mr., on fruit-trees in Ame-
rica, 6Q.

Dragon-flies, intestines of, 147.

Drift-timber, 326,

Driver-ant, 232.

Drones killed by other bees, 164.

Duck, domestic, wings of, reduced, S,

, beak of, 183.

, logger-headed, 140.

Duckweed, 344.

Dugong, affinities of, 365.

Dung-beetles with deficient tarsi, 108,

Dytiscus, 345.

E.

Earl, Mr. W., on the Malay Archipe-
lago, 351.

Ears, drooping, in domestic animals, 8.

, rudimentary, 400.

Earth, seeds in roots of trees, 326.

charged with seeds, 328.

Echinodermata, their pedicellarire,
191.

Eciton, 230.

Economy of organisation, 117.

Edentata, teeth and hair, 115.

, fossil species of, 417.

Edwards, Milne, on physiological
division of labour, 89.

— — , on gradations of structure, 156.

, on embryological characters,

368.

Eggs, young birds escaping from, 68.

Egypt, productions of, not modified.!
169. j

Electric organs, 150. I

Elephant, rate of increase, 51. \

, of Glacial period, 113.

Embryology, 386. ,

Eozoon Canadense, 287.

Epilepsy inherited, 108.

Existence, struggle for, 48.

, conditions of, 167.

Extinction, as bearing on natura
selection, 96.

of domestic varieties, 93.

, 293.

EYE.

INDEX.

GALEOriTIIECUS.

447

Eye, structure of, 144.

, correction for aberration, 163.
Eyes reduced in moles, 110.

F.

Fabre, M., on hymenoptera fighting,

69.

, on parasitic sphex, 216.

, on Sitaris, 394.

Falconer, Dr., on naturalisation of

plants in India, 51.
, on elephants and mastodons,

306.

and Cautley, on mammals of

sub-Himalayan beds, 311.

Falkland Islands, wolf of, 351.

Faults, 268.

Faunas, marine, 317.

Fear, instinctive, in birds, 211.

Feet of birds, young molluscs ad-
hering to, 345.

Fertilisation variously effected, 154,
161.

Fertility of hybrids, 238.

, from slight changes in con-
ditions, 252.

Fertility of crossed varieties, 255.

Fir-trees destroyed by cattle, 56.

, pollen of, 164.

Fish, flying, 140.

, teleostean, sudden appearance

of, 285.

, eating seeds, 327, 346.

fresh-water, distribution of,

343.
Fishes, ganoid, now confined to fresh

water, 83.

, electric organs of, 150.

, ganoid, living in fresh water,

296.
-, of southern hemisphere, 338.

Flat-fish, their structure, 186.
Flight, powers of, how acquired, 140.
Flint-tools, proving antiquity of man,

13.
Flower, Prof., on the Larynx, 190.

, on Halitherium, 302.
■ , on the resemblance between

the jaws of the dog and Thyla-

cinua, 375.
, on the homology of the feet of

certain marsupials, 382.
Flowers, structure of, m relation to

crossing, 73.

Flowers, of compositic and umbelli"
fer£B, 116, 173.

, beauty of, 161.

, double, 230.

Flysch formation, destitute of or-
ganic remains, 271.

Forbes, Mr. D., en glacial action in

^ the Andes, 335.

, E., on colours of shells, 107.

, on abrupt range of shells in

depth, 135.

, on poorness of paljeontological

collections, 270.

, on continuous succession ot

genera, 293.

, on continental extensions, 323.

-, on distribution during Glacial

period, 330.
-, on parallelism in time and

space, 361.
Forests, changes in, in America, 58.
Formation, Devonian, 305.

, Cambrian, 287.

Formations, thickness of, in Britais^

268, 269.

, intermittent, 277.

Formica rufescens, 216.

, sanguinea, 217.

, flava, neuter of, 231.

Forms, lowly organised, long ea-

during, 99.
Frena, ovigerous, of cirripedes, 148.
Fresh-water productions, dispersal

of, 343.
Fries, on species in large genera

being closelv allied to other spedos,

45.
Frigate-bird, 142.
Frogs on islands, 350.
Fruit-trees, gradual improvement of,

27.

in United States, 66.

, varieties of, acclimatised in

United States, 114.
Fuci, crossed, 243, 249.
Fur, thicker in cold climates, 107.
Furze, 388..

G.

Galapagos Archipelago, birds of, 348,

, productions of, 353, 355,

Galaxias, its wide range, 343.
Galeopithecus, 139.

b

448

GAME.

INDEX.

MELIANTIIEMUM.

Game, increase of, checked ty ver-
min, 55.

Gartner, on steiility of hybrids, 2o7,
241.

, on reciprocal crosses, 243.

, on crossed maize and verbas-
cum, 257, 258.

, on comparison of hybrids and

mongrels, 259, 260.

Gaudry, Prof., on intermediate genera
of fossil mammals in Attica, 301.

Geese, fertility when crossed, 240.

, upland, 142.

Geikie, Mr., on subaerial denudation,
267.

Genealogy, important in classifica-
cation, 369.

Generations, alternate, 387.

Geoffroy St. Hilaire, on balancement,
117.

— — , on homologous organs, 382.

, Isidore, on variability of re-
peated parts, 118.

, on correlation, in monstrosi-
ties, 9.

on correlation, 115.

, on variable parts being often

monstrous, 122.
Geographical distribution, 316.
Geography, ancient, 427.
Geology, future progress of, 427.
, imperfection of the record,

427.
Gervais, Prof., on Typotherium, 302.
Giraffe, tail of, 157.

, structure of, 177.

Glacial period, 330.

, affecting the North and South,

335.
-Glands, mammary, 189.
Gmelin, on distribution, 330,
Godwin-Austen, Mr., on the Malay

Archipelago, 280.
Goethe, on compensation of growth,

117.
Gomphia, 174.
Gooseberry, grafts of, 246.
Oould, Dr. Aug. A., on land-shells,

?o3.

, Mr., on colours of birds, 107.

< , on instincts of cuckoo, 214.

, on distribution of eenera of

birds, 358.
Gonrds, crossed, 258

Graba, on the Uria lacrymans, 72.

Grafting, capacity of, 245, 246.

Granite, areas of denuded, 274.

Grasses, varieties of, 88.

Gray, Dr. Asa, on the variability of
oaks, 40.

, on man not causing varia-
bility, 62.

, on sexes of the holly, 74.

, on trees of the United State?,

79.

— , on 'naturalised plants in the
United States, 89.

— , on asstivation, 174.

— , on Alpine plants, 330.

— , on rarity of intermediate va-
rieties, 136.
-, Dr. J. E., on striped mule, 128.

Grebe, 142.

Grimm, on asexual reproduction, 387.

Groups, aberrant, 378.

Grouse, colours of, 66.

, red, a doubtful species, 38.

Growth, compensation of, 117.
Giinther, Dr., on fiat-fish, 187.

, on prehensile tails, 189.

, on the fishes of Panama, 317.

, on the range of fresh-water

fishes, 343.

on the limbs of Lepidosirea,

399.

H.

Haast, Dr., on glaciers of New Zea-
land, 335.

Habit, effect of, under domestica-
tion, 8.

' , effect of, under nature, 108.

, diversified, of same species, 141.

Hackel, Prof, on classification and
the lines of descent, 381.

Hair and teeth, correlated, 115.

Halitherium, 302.

Harcourt, Mr. E. V,, on the birds of
Madeira, 348.

Hartung, M., on boulders in the
Azores, 328.

Hazel-nuts, 325.

Hearne, on habits of bears, 141.

Heath, changes in vegetatiou, 55.

Heer, Oswald, on ancient cultivatec
plants, 13.

, on plants of Madeira, 83.

Helianthemum, 174.

HELIX.

INDEX.

INDIVIDUALS.

449

Helix pomatia, 353.

Helraholtz, M., on the imperfection

of the human eye, 163.
Helosciadium, 325.
Hemionus, striped, 128.
Hensen, Dr., on the eyes of Cepha-

lopods, 152.
Herbert, W., on struggle for exist-
ence, 49.

, on sterility of hybrids, 238.

Hector, Dr., on glaciers of New Zea-
land, 335.
Hermaphrodites crossing, 76.
Helix, resisting salt water, 353.
Heron eating seed, 346.
Heron, Sir R., on peacocks, 70.
Heusin^er, on white animals poi-
soned by certain plants, 9.
Hewitt, Mr., on sterility of first

crosses, 249.
Hildebrand, Prof, on the self-ste-
rility of Corydalis, 238.
Hilgendorf, on intermediate varie-
ties, 275.
Himalaya, glaciers of, 335.

, plants of, 337.

Hippeastrum, 238.
Hippocampus, 189.
Hofmeister, Prof, on the movements

of plants, 197.
Hollv-trees, sexes of, 73.
Hooker, Dr., on trees of New Zea-
land, 78.
• , on acclimatisation of Hima-
layan trees, 112.

, on flowers of umbelliferae, 116.

, on the position of ovules, 172.

• , on glaciers of Himalaya, 335.

, on algae of New Zealand, 338.

• , on vegetation at the base of

the Himalaya, 338.

' , on plants of Tierra del Fuego,

336.
- , on Australian plants, 337, 355.
, on relations of flora of Ame-
rica, 340.
?s— — , on flora of the Antarctic lands.

341, 354.
.' , on the plants of the Gala-
pagos, 349, 354.
—— , on glaciers of the Lebanon,
335.
> or. man not causing variability

63.

Hooker, Dr., on plants of mountains

of Fernando Po, 337.
Hooks on palms, 158.

on seeds, on islands, 349.

Hopkins, Mr., on denudation, 274.
Hornbill, remarkable instinct of

234.
Horns, rudimentary, 400.
Horse, fossil, in La Plata, 294.

, proportions of, when vonng,

392. ^'

Horses destroyed by flies in Para-
guay, 56.

, striped, 128.

Horticulturists, selection applied bv.
23. • '

Huber, on cells of bees, 224.

, P., on reason blended with,

instinct, 205.

, on habitual nature of instincts,

206.

, on slave-making ants, 216.

, on Melipona domostica, 220.

Hudson, Mr., on the Ground-Wood-
pecker of La Plata, 142.

, on the Molothrus, 215.

Humble-bees, cells, of, 221.
Hunter, J., on secondary sexual

characters, 119.
Hutton, Captain, on crossed geese,

240.
Huxley, Prof., on structure of her-
maphrodites, 79.

, on the affinities of the Sirenia.

302.

, on forms connecting birds and

reptiles, 302.

, on homologous organs, 386.

, on the development of aphis,

390.
Hybrids and mongrels compared,

259.
Hybridism, 235.
Hydra, structure of, 147.
Hymenoptera, fighting, 69.
Hymenopterous iniect, diving, 142.
Hyoseris, 173.

Ibla, 118.

Icebergs transporting seeds, 329.
Increase, rate of, 50.
Individuals, numbers favcnrable to
selection, 80.

2 G

450

INDIVIDUALS.

INDEX.

LUCAS.

Individuals, many, whether simulta-
neously created, o22

Inheritance, laws of, 10.

, at corresponding ages, 10, 67.

Insects, colour of, fitted for their
stations, Q6.

, sea-side, colours of, 107.

, blind, in caves, 110.

, luminous, 151.

, their resemblauco to various

objects, 181.

, neuter, 230.

Instinct, 205.

, not varying simultaneously

with structure, 229.

Instincts, domestic, 209.

Intercrossing, advantages of, 76, 251.

Islands, oceanic, 347.

Isolation favourable to selection, 81.

J.

Japan, productions of, 334.

Java, plants of, 337.

Jones, Mr. J. M., on the birds of
Bermuda, 348.

Jourdain, M., on the eye-spots of
star-fishes, 144.

Jukes, Prof., on subaerial denuda-
tion, 267.

Jussieu, on classification, 367.

K.

Kentucky, caves of, 111.

Kerguelen-land, flora of, 341, 354.

Kidney-bean, acclimatisation of, 114.

Kidneys of birds, 115.

Kirby, on tarsi deficient in beetles,
108.

Knight, Andrew, on cause of varia-
tion, 5.

Kolreuter, on Intercrossing, 76.

, on the barberry, 77.

, on sterility of hybrids, 237.

, on reciprocal crosses, 243.

-, on crossed varieties of nico-

tiana, 258.

, on crossing male and herma-
phrodite flowers, 397.

L.

Lamarck, on adaptive characters,

373.
Lanctlet, 99.

eyes of, 145

Landois, on the development of the

wings of insects, 148.
Land-shells, distribution of, 353.

, of Madeira, naturalised, 357.

, resisting salt water, 353.

Languag26, classification of, 371.
Lankester, Mr. E. Ray, on Longevity

169.

, on homologies, 385.

Lapse, gre:it, of time, 266.

LarviE, 388, 389.

Laurel, nectar secreted by the leavcsr,

73.
Laurentian formation, 287.
Laws of variation, 106.
Leech, varieties of, 59.
Leguminosffi, nectar secreted by

glands, 73.
Leibnitz' attack on Newton, 421.
Lepidosiren, 83, 303.
■ , limbs in a nascent condition,

398, 399.
Lewes, Mr. G. H., on species not hav-
ing changed in Egypt, 169.

, on the Salamandra atra, 397.

, on many forms of life having

been at first evolved, 425.
Life, struggle for, 49.
Lingiila, Silurian, 286.
Linnajus, aphorism of, 365.
Lion, mane of, 69.

, young of, striped, 388.

Lobelia fulgens, 57, 77.

• ■■ , sterility of crosses, 238.

Lockwood, Mr., on the ova of the

Hippocampus, 189.
Locusts transporting seeds, 327.
Logan, Sir W., on Laurentian forma-
tion, 287.
Lowe, Rev. R. T., on locusts visiting

Madeira, 327.
Lowness of structure connected with

variability, 118.
, related to wide distribution,

359.
Lubbock, Sir J., on the nerves of

coccus, 35.
, on secondary sexual characters,

124.
.. on a diving hymenopterous

insect, 142.
— — , on affinities, 280.
. - ■ ■, on metamorphoses, 386, 389,
Lucas, Dr. P.-j on inheritance, 9.

LUCAS.

INDEX.

MOXS.

451

Incas, Dr. P., on resemblance of child

to parent, 261.
Lund and Clausen, on fossils of

Brazil, 310.
Lyell, Sir C, on the struggle for

existence, 49.
, on modern changes of the

earth, 75.
, on terrestial animals not having

been developed on islands, 180.
-, on a carboniferous land-shell.

beneath Silurian

271.

— , on strata
system, 287.

— , on the imperfection of the
geological record, 289.

— , on the appearance of species,
289.

— , on Barrande's colonies, 291.

— , on tertiary formations of
Europe and North America, 298.

— , on parallelism of tertiary for-
mations, 301.

— , on transport of seeds by ice-
oergs, 328.

— , on great alternations of cli-
mate, 342.

on the distribution of fresh-

water shells, 345.
, on land-shells of Madeira,

357.
Lyell and Dawson, on fossilized trees

*in Nova Scotia, 278.
Lythrum salicaria, trimorphic, 254.

M.

Macleay, on analogical characters,

373.
Macrauchenia, 302.
McDonnell, Dr., on electric organs,

150.
Madeira, plants of, 83.

, beetles of, wingless, 109.

, fossil land-shells of, 311.

, birds of, 348.

Magpie tame in Norway, 209,

Males fighting, 69.

Maize, crossed, 257.

Malay Archipelago compared with

Europe, 280.

, mammals of, 352.

Malm, on flat-fish, 186.
Malpighiacese, small imperfect flowers

of, 173.

Malpighiaceae, 367.

Mammas, their development, 189.

, rudimentary, 397.

Mammals, fossil, in secondarv for-
mation, 283.

, insular, 351,

Man, origin of, 428.

Manatee, rudimentaiy nails of, 40t?»

Marsupials of Australia, 90.

, structure of their feet, 382.

, fossil species of, 310.

Martens, M., experiment on seeds, 325,
Martin, Mr. W. C, on striped mules,

129.
Masters, Dr., on Saponaria, 174.
Matteucci, on the electric organs of

rays, 150.
Matthiola, reciprocal crosses of, 244.
Maurandia, 197.
Means of dispersal, 323.
Melipona domestica, 220.
Merrell, Dr., on the American cuckoo,

212.
Metamorphism of oldest rocks, 287.
Mice destroying bees, 56.

, acclimatisation of, 113.

, tails of, 189.

Miller, Prof., on the cells of bees,

221, 224.
Mirabilis, crosses of, 243.
Missel-thrush, 59.
Mistletoe, complex relations of, 2.
Mivart, Mr., on the relation of hair

and teeth, 115.
, on the eyes of cephalopods,

151.

— , various objections to Natural
Selection, 176,.

— , on abrupt modifications, 201.
— , on the resemblance of the

mouse and antechinus, 373.

Mocking-thrush of the Galapagos,
357.

Modification of species not abrtipt,
424.

Moles, blind, 110.

Molothrus, habits of, 215.

Mongrels, fertility and sterility of
255.

and hybrids compared, 259

Monkeys, fossil, 284, 285.

Monachanthus, 372.

Mons, Van, on the origin of fruit-
trees, 21.

452

MONSTROSITIES.

INDEX.

OSTBICH.

Monstrosities, 33.

Moquin-Taudon, on sea-side plants,

107.
Morphology, 382.

Morren, on the leaves of Oxalis, 197.
Moths, hybrid, 240.
Mozart, musical powers of, 206.
Mud, seeds in, 345.
Mules, striped, 129.
Miiller, Adolf, on the instincts of the

cuckoo, 213.
Miiller, Dr. Ferdinand, on Alpine

Australian plants, 337.
Miiller, Fritz, on dimorphic crus-
taceans, 35, 233.
— — , on the lancelet, 99.

, on air-breathing crustaceans,

152.
— — , on climbing plants, 197.

, on the self-sterility of orchids,

238.

, on embryology in relation to

classification, 368.
, on the metamorphoses of crus-
taceans, 390, 395.

, on terrestrial and fresh-water

organisms not undergoing any me-
tamorphosis, 394.
Multiplication of species not indefi-
nite, 101.
Murchison, Sir R., on the forma-
tions of Russia, 272.

, on azoic formations, 286.

, on extinction, 293.

Murie, Dr., on the modification of ths

skull in old age, 149.
Murray, Mr. A., on cave-insects. 111.
Mustela vison, 138.
Myanthus, 372.
Myrmecocystus, 231.
Myrmica, eyes of, 232.

N.

Nageli, on morphological characters,

170.
Nails, rudimentary, 400.
NathuGius, Von, on pigs, 159.
Natural history, future progress of,

426.

selection, 62.

— — system, 364.

Naturalisation of forms distinct from

the indigenous species, 89.

Naturalisation in New Zealand^ 163.

Naudin, on analogous variations in
gourds, 125.

, on hybrid gourds, 258.

, on reversion, 260.

Nautilus, Silurian, 286.

Nectar of plants, 73.

Nectaries, how formed, 73.

Nelumbium luteum, 346.

Nests, variation in, 208, 228, 234.

Neuter insects, 230, 231.

Newman, Col., on humble-bees, 57.

New Zealand, productions o£^ not
perfect, 163.

, naturalised products of, 309.

, fossil birds of, 310.

, glaciers of, 335.

, crustaceans of, 338.

, algse of, 338.

, flora of, 354.

, number of plants of, 347

Newton, Sir I., attacked for irre-
ligion, 421.

, Prof., on earth attached to 3

partridge's foot, 328. ^

Nicotiana, crossed varieties of, 258.

, certain species very steiile,

243.

Nitsche, Dr., on the Polyzoa, 193.

Noble, Mr., on fertility of Rhodo-
dendron, 239.

Nodules, phosphatic, in azoic rockg,
287.

0.

Oaks, variability of, 40.

Ononis, small imperfect flowers of,

172.
Onites appelles, 108.
Orchids, fertilisation of, 154.
— — , the development of fheit

flowers, 195.

, forms of, 372.

Orchis, pollen of, 151.

Organisation, tendency to advance, 97'.

Organs of extreme perfection, 143.

, electric, of fishes, 150.

of little importance, 156.

, homologous, 382.

, rudiments of, and nascent, 397

Ornithorhynchus, 83, 367.

, mammae of, 190.

Ostrich not capable of flight, 180.

OSTRICH.

INDEX.

POINTER.

453

Ostrich, habit of laying eggs *. :gether

215.

, American, two species of, 318.

Otter, habits of, how acquired, 138.

Ouzel, water, 142.

Owen, Prof., on birds not flying, 108.

, on vegetative repetition, 118.

, on variability of unusually

developed parts, 119.

, on the eyes of fishes, 145.

, on the swim-bladder of fishes,

148.

, on fossil horse of La Plata,

294. '

, on generalized form, 301.

, on relations of ruminants and

pachyderms, 303.
, on fossil birds of New Zealand,

310. '

, on succession of types, 310.

, on affinities of the duoi-onsr

365. " ^

, on homologous organs, 383.

, on the metamorphosis of ce-

phalopods, 390.

P.

Pacific Ocean, faunas of, 317.

Pacini, on electric organs, 151.

Paley, on no organ formed to give
pain, 163.

Pallas, on the fertility of the domes-
ticated descendants of wild stocks
241. '

Palm with hooks, 158.

Papaver bracteatum, 174.

Paraguaj', cattle destroyed by flies,
56.

Parasites, 215.

Partridge, with ball of earth attached
to foot, 328.

Parts greatly developed, variable,
119. '

Parus major, 141.

Passiflora, 238.

Peaches in United States, 6^

Pear, grafts of, 246.

Pedicellariae, 191.

Pelargonium, flowers of, 116.

• , sterility of, 239.

Pelvis of women, 115.

Peioria, 116.

Period, glacial, 330.

Petrels, habits of, 142.

Phasianus, fertility of hybrids, 240.

Pheasant, young, wild, 211.

Pictet, Prof., on groups of species

suddenly appearing, 282.

, on rate of organic change, 291.

, on continuous succession cf

genera, 293.
, on change in latest tertiary

forms, 278.
, on close alliance of fossils in

consecutive formations, 306.

, on early transitional links, 283.

Pierce, Mr., on varieties of wolves,

71.
Pigeons with feathered feet and skin

between toes, 9.
, breeds described, and origin of,

15.

, breeds of, how produced, 28.

30. r , ,

, tumbler, not being able to get

out of egg, 68.

, rc^-erting to blue colour, 127.

, instinct of tumbling, 210.

— — , young of, 392.

Pigs, black, not affected by the paint-
root, 9.

, modified by want of exercise,

159.

Pistil, rudimentary, 397.

Plants, poisonous, not affecting cer-
tain coloured animals, 9.

, selection applied to, 27.

, gradual improvement of, 27.

, not improved in barbarous

countries, 27.

, dimorphic, 35, 253.

, destroyed by insects, 13.

, in midst of range, have

struggle with other plants, 60.

, nectar of, 73.

, fleshy, on sea-shores, 107.

, climbing, 147, 196.

fresh-water, distribution

to

o{.

, low in scale, widely distri-

34:

low in

butcd, 359.
Pleuronectidae, their structure, 186.
Plumage, laws of change in sexes of

birds, 70.
Plums in the United States, 66,
Pointer dog, origin of, 25.
, habits of, 210.

454

POISOX.

INDEX.

SEA-WATER.

Poison not affecting certain coloured

animals, 9.
i , similar effect of, on animals

and plants, 425.
Pollen of fir-trees, 164.
transported by rarious means,

154, 161.
PoUinia, their development, 1 95.
Polyzoa, their avicularia, 193.
Poole, Col., oa striped hemionus,

128.
Potamogeton, 346.
Pouchet, on the colours of flat-fish,

188.
Prestwich, Mr., on English and

French eocene formations, 300.
Proctotrupes, 142.
Proteolepas, 118.
Proteus, 112.

Psychology, future progress of, 428.
Pyrgoma, found in the chalk, 284.

Q.

Quagga, striped, 129.

Quatrefages, M., on hybrid moths,

240.
Quercus, variability of, 40.
Quince, grafts of, 246.

B.

Rabbit, dispositiou of young, 211.

Races, domestic, characters of, 12

Race-horses, Arab, 26

, English, 323.

Radcliffe, Dr., the electrical organs
of the torpedo, 150.

Ramond, on plants of Pyrenees, 331.

Ramsay, Prof., on subaerial denu-
dation, 267.

, on thickness of the British

formations, 268, 269.

, on faults, 268.

Ramsay, Mr., on instincts of cuckoo,
213.

Ratio of increase, 50.

Rats supplanting each other, 59.

, acclimatisation of, 113.

, blind, in cave, 110.

Rattle-snake, 162.

Reason and instinct, 205.

Recapitulation, general, 404.

Recriprocity of crosses, 243.

Record, geological, imperfect, 264.

Rengger, on flies destroying cattle.
56.

Reproduction, rate of, 50.

Resemblance, protective, of insects,
181.

to parents in mongrels and

hybrids, 260.

Reversion, law of inheritance, 11.

, in pigeons, to blue colour, 127.

Rhododendron, sterility of, 239.

Richard, Prof, on Aspicarpa, 367.

Richardson, Sir J., on structure of
squirrels, 139.

, on fishes of the southern hemi-
sphere, 338.

Robinia, gi'afts of, 246.

Rodents, blind, 110.

Rogers, Prof, Map of N. America,
274.

Rudimentary organs, 397.

Rudiments important for classifica-
tion, 367.

Riitimeyer, on Indian cattle, 14,
241.

S.

Salamandra atra, 397.

Saliva used in nests, 228.

Salvin, Uv., on the beaks of ducks,

184.
Sageret, on grafts, 246.
Salmons, males fighting, and hookec

jaws of, 69.
Salt water, how far injurious to

seeds, 325.
not destructive to land-shells,

353.
Salter, Mr., on early death of hybrid

embryos, 249.
Saurophagus sulphuratus, 141.
Schacht, Prof, on Phyllotaxy, 173.
Schiodte, on blind insects, 110.

, on flat-fish, 186.

Schlegel, on snakes, 115.

Schbbl, Dr., on the ears of mice, 172

Scott, J., Mr., on the self-sterility <

orchids, 238.
, on the crossing of varieties

verbascum, 258.
Sea-water, how far injurious

seeds, 325.
not destructive to land-shelj

353.

SEBUTGIIT.

INDEX.

STOCKS.

455

Sebiight, Sir J. on crossed animals,

15.
Sedgwick, Prof,, on groups of species

suddenly appearing, 282.
Seedlings destroyed by insects, 53.
Seeds, nutriment in, 60.

, winged, 117.
, means of dissemination, 154,

161, 327, 328.
, power of resisting salt water,

325.
, in crops and intestines cf

birds, 326, 327.

, eaten by fish, 327, 346.

in mud, 345.

7 •

, hooked, on islands, 349.

Selection of domestic products, 22.

, principle not of recett criirin,

27.

unconscious, 27.

-, natural, 62^
-, sexual, 69.
-, objections to term, 63.
natural, has not induced

ste-

rility, 247.
Sexes, relations of, 69.
Sexual characters variable, 123.
— — selection, 69.
Sheep, Merino, their selection, 23.
— — , two sub-breeds, unintentionally

produced, 26.
— — , mountain varieties of, 59.
Shells, colours of, 107.

■ , hinges of, 154.

" , littoral, seldom embedded, 270.

, fresh-water, long retain the

same forms, 308.

■ , fresh-water, dispersal of, 344.

, of Madeira, 349.

■ , land, distribution of, 349.

, land, resisting salt water, 353.

Shrew-mouse, 373.
Silene, infertility of crosses, 243.
Silliman, Prof., on blind rat, 110.
Sirenia, their affinities, 302.
Sitaris, metamorphosis of, 394.
Skulls of young mammals, 159, 384.
■^lave-making instinct, 216.
i jmith. Col. Hamilton, on striped

horses, 129.
' , Mr. Fred., on slave-making

aiits, 217.

, on neuter ants, 231.

Smitt, Dr., on the Polyzoa, 193.

Snake with tooth for "cutting through

egg-shell, 214.
Somerville, Lord, on selection of

sheep, 23.
Sorbus, grafts of, 246.
Sorex, 373.

Spaniel, King Charles's breed, 25.
Specialisation of organs, 98.
Species, polymorphic, 35.

, dominant, 43.

, common, variable, 42.

in large genera variable, 44.

" » groups of, suddenly appearinrr,

282,285.

beneath Silurian formations,

287.

successively appearing, 290.

changing simultaneously

throughout the world, 297.

Spencer, Lord, on increase in size of
cattle, 26.

, Herbert, Mr., on the first steps

in differentiation, 100.
, on the tendency to an equili-
brium in all forces, 252.
Sphex, parasitic, 216.
Spiders, development of, 390.
Sports in plants, 8.
Sprengel, C. C, on crossing, 76.

• , on ray-florets, 116.

Squalodon, 302.

Squirrels, gradations in structure,

139.
Staffordshire, heath, changes in, 55.
Stag-beetles, fighting, 69.
Star-fishes, eyes of, 144.

, their pedicellarias, 192.

Sterility from changed conditions of
life, 7.

of hybrids, 236.

, laws of, 241.

— — , causes of, 247.

■ from unfavourable conditions,

250.
— — not induced through natural

selection, 247.
St. Helena, productions of, 347.
St. Hilaire, Aug., on variability of
certain plants, 174.
, on classification, 368.
St. John, Mr., on habis of eats. 209.
Sting of bee, 163.

Stocks, aboriginal, of domestic ani
mals, 14.

456

STRATA.

INDEX.

LTILITY

Strata, thickness of, in Britain, 268,

269.
Stripes on horses, 128.
Structure, degrees oi utility of, 159.
Struggle for existence, 48,
Succession, geological, 290,

of types in same arexs, 310.

Swallow, one species supplanting

another, 59.
Swaysland, Mr., on earth adhering to

the feet of migratory birds, 328.
Swifts, nests of, 228.
Swim-bladder, 148.
Switzerland, lake habitations of, 13.
System, natural, 364.

T.

Tail of giraffe, 157.

— — of aquatic animals, 157.

, prehensile, 188.

, rudimentary, 400.

Tanais, dimorphic, 36.

Tarsi, deficient, 108.

Tausch, Dr., on umbelliferse, 173.

Teeth and hair correlated, 115.

, rudimentary, in embryonic,

calf, 397, 420.
Tegetmeier, Mr., on cells of bees,

222, 226.
Temminck, on distribution aiding

classification, 369.
Tendrils, their development, 196.
Thompson, Sir W., on the age of the
habitable world, 286.

, on the consolidation of the

crust of the earth, 409.
Thouin, on grafts, 246.
Thrush, aquatic species of, 142.

, mocking, of the Galapagos, 356

, young of, spotted, 388.

, nest of, 234.

Thuret, M., on crossed fuci, 243.
Thv/aites, Mr., on acclimatisation,

112.
Thylacinus, 374.
Tierra del Fuego, dogs of, 21 1.

, plants of, 341.

Timber-drift, 326.
Time, lapse of, 266.
by itself not causing modifica-
tion, 81.
Titmouse. 141

Toads on islands, 350.

Tobacco, c-ossed varieties cf, 258.

Tomes, Mr., on the distribution of

bats, 351.
Transitions in varieties rare, 134.
Traquair, Dr., on flat-fish, 188.
Trautschold, on intermediate varie-
ties, 275.
Trees on islands belong to peculiar
orders, 350.

with separated sexep, 78.

Trifolium pratense, 57, 75,

incarnatum, 75.

Trigonia, 296.
Trilobites, 286.

, sudden extinction of, 297.

Trimen, Mr., on imitating-insec'.8,

377.
Trimorphism in plants, 35, 252.
Troglodytes, 234.
Tuco-tuco, blind, 110.
Tumbler pigeons, habits of, heredi-
tary, 210.

, young of, 392.

Turkey-cock, tuft of hair on bseast,
70.

, naked skin on bead, 158.

, young of, instinctively wild,

211.
Turnip and cabbage, analogous vari-
ations of, 125.
Type, unity of, 166, 1(57.
Types, succession of, in same areas,

310.
Typotherium, 302.

TJ.

Udders enlarged by use, 8.

, rudimentary, 397.

Ulex, young leaves of, 388.
Umbeliifera, flowers and seeds of,

116.

, outer and inner florets of, 173.

Unity of type, 166, 167.

Uria'lacrymans, 72.

Use, effects of, under domestication

8.
, effects of, in a state of nature

Utility, how far important m tn»
construction of each part, 159 ■

VALENCIENNES.

INDEX.

WOLF.

457

V.

Valenciennes, on fresh-water fish, 344.
Variability of mongrels and hybrids,

259.
Variation under domestication, 5.
caused by reproductive system

being affected by conditions of

life, 7.

under nature, 33.

, laws of, 106.

, correlated, 9, Hi, 159.

Variations appear at corresponding

ages, 10, 67.
' analogous in distinct species,

124.
Varieties, natural, 32.

, struggle between, 59.

, domestic, extinction of, 86,

, transitional, rarity of, IS-t.

, when crossed, fertile, 257.

, when crossed, sterile, 256.

, classification of, 371.

Verbascum, sterility of, 238.

■ , varieties of, crossed, 258.

Verlot, M., on double stocks, 230.
Verneuil, M. de, on the succession of

species, 299.
Vibracula of the Polyzoa, 193.
Viola, small imperfect flowers of, 173.

, tricolor, 57.

Virchow, on the structure of the

crystalline lens, 145.
Virginia, pigs of, 66.
Volcanic islands, denudation of, 268.
Vulture, naked skin on head, 158.

W.

Wading-birds, 345.

Wagner, Dr., on Cecidomyia, 387

Wagner, Moritz, on the importance
of isolation, 81.

Wallace, Mr., on origin of species, 1.

• , on the limit of variation under

domestication, 31.

,' , on dimorphic lepidoptera, 36,

232.

— , on races in the Malay Archi-
pelago, 37.

— t on ttiQ improvement of the eye,
145.

Wallace, Mr., on the walking-stick
insect, 182.

— — -, on laws of geographical distri-
bution, 322.

, on the Malay Archipelago, 351.

, on mimetic animals, 377.

Walsh, Mr. B. D., on phytophagic
forms, 38. r j i ^

, on equable variability, 125.

Water, fresh, productions of, 343.
Water-hen, 143.

Waterhouse, Mr., on Australian mar-
supials, 90.

, on greatly developed parts

being variable, 119.

, on the cells of bees, 220.

y on general affinities, 379.

Water-ouzel, 142.

Watson, Mr. H. C, on range of va-
rieties of British plants, 37, 46.

, on acclimatisation, 112.

, on flora of Azores, 328.

, on Alpine plants, 331.

, on rarity of intermediate va-
rieties, 136.

, on convergence, 100.

, on the indefinite multiplication

of species, 101.
Weale, Mr., on locusts transporting

seed«!, 327.
Web of feet in water-birds, 142.
Weismann, Prof., on the causes of
variability, 6.

, on rudimentary organs, 400.

West Indian Islands, mammals of.
352. '

Westwood, on species in large genera
being closely allied to others, 45.

, on the tarsi of Engida, 124.

, on the antenna; of hymeno-

pterous insects, 366.
Whales, 182.
Wheat, varieties of, 88.
White Mountains, flora of, 330.
Whittaker, Mr., on lines of escarp-
ment, 267.
Wichura, Max, on hybrids, 249 251,

260.
Wings, reduction of size, 109.

of insects homologous with

branchiae, 148.

, rudimentary, in insects, 397,

Wolf crossed with dog, 210.
• of Falkland Isles, 351.

2 H

A^^^^^jpu^

458

WOLLASTON.

INDEX.

ZEUQLOIK)S

Wollaston, Mr., on varieties of in-
sects, 38. « 1. n •
^ on fossil vai'icties of shells in

Madeira, 42.

^ on colours of insects on sea-
shore, 107.

on wingless beetles, 109.

\ on rarity of intermediate va-
rieties, 136. ^ _

on insular insects, o47.

\ on land-shells of INIadeira, natu-
ralised, 357.

Wolves, varieties of, 71. , ,^ ,

Woodcock with earth attached to leg,

328.
Woodpecker, habits of, Ul.

sreen colour of, 158.

Woodward, Mr., on the duration of

specific forms, 276.

. , on Pyrgoma, 284. _

. on the continuous succession ot

geueii

293.

_-, on 'the succession of types. 311.

World, species changing sirauHHne-
ously throughout, 297.

Wrens, nest of, 234. ^

Wright, Mr. Chauncey, on the giratte,
1 78

on abrupt modifications, 203.

W^mau, Prof., on correlation of co-
lour and effects of poison, 9.

, on the cells of the bee, 222.

Y.

Youatt, Mr., on selection, 23.

J on sub-breeds of sheep, 26.

\ on rudimentary horns in yonog

cattle, 400.

Z.

Zanthoxylon, 174.
Zebra, stripes on, 128.
Zeuglodon, 302.

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Japan: Its History, Traditions, and Religions. With

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REJECTED ADDRESSES (The). By Jambs and Horace Smith.

Woodfuts. Post 8vo. 3s. <od. \ or Vovular Edition, Fcap. 8vo. Is.
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REVISED YERSION OF N.T. [See Beckett— Burqon— Cook.]
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ROMILLY (Hugh H.). The Western Pacific and New Guinea.

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SELBOKNE (Lori.). Notes on some Passages in the Liturgical

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^""^""fer 2? V '''^'' ^^^^- ^^^^^^^ ^y "^^^-° LlDBON.

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au A w fm o ^^'^ Portrait. Crown Svo. 12s. ^

»HAW (I.B.). Manual of English Literature. Post Svo. 7s 6d
' "ph Fw™^""^ ®^ English Literature. Selected from the

Chief Writers. Post Svo. Is. 6d.

and^R!f.fr?-T^^'^^ ^^ ^'^^ '^^"*^^' Yarkand, and Kashgar,

inu^ti\rn".''ro"'^167" '"' ^*-^^— Pass. With Map ^and'
SIEMENS (Sir Wh.), CE.* Life of. By Wm. Pole, C.E. Svo

RTK«RA T^r^tl^^'^l?'' ^''^°' ^^^ ^^P^^^ ^f- 2 vols. Svo.
SIERRA LEONE ; Described in Letters to Friends at Home. By
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^^^^IHu ^?o"''t ^«"«^i^"*i«^ ^^d Practice of Courts-Mar.
SMILES' (Samdel*'lL.D.) WORKS;—

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caJJU^^^JulcL ^

26 LIST OF WORKS

SMILES' (Samuel, LL.D.) WO^K^— continued.

Life and Labour ; or, Characteristics of Men of Industry,

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George Stephenson. PoBt 8vo. 2s. Qd.
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Self-Help. With Illustrations of Conduct and Persever-
ance. Post 8vo. 6s.
Character. A Book of Noble Characteristics. Post 8vo. 6s.
Thrift. A Book of Domestic Counsel. Post 8vo. 68.
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Post 8vo. 6s.

Industrial Biography; or, Iron-Workers and Tool-Makers.

Post 8vo. 6s.

Men of Invention and Industry. Post 8vo. 6s.
.— -^ Boy's Yoyage Round the World. Illustrations. Post 8vo. 6s.

SMITH (Dr. George) Student's Manual of the Geography of British

India, Physical and Political. With Maps. Post 8vo. 7s. 6d.

Life of John Wilson, D.D. (Bombay), Missionary and

Philanthropist. Portrait. Post 8vo. 9s.
Life of Wm. Carey, D.D., 1761-1834. Shoemaker aa«l

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of Fort "William, Calcutta. Portrait and Illustrations. 8vo. 16s.
— (Philip). History of the Ancient World, from the Creation

to the Fall of the Roman Empire, a.d. 476. 3 Vols. Svo. 31«. 6d.

SMITH'S (Dr. Wm.) DICTIONARIES:—

Dictionary of the Bible; its Antiquities, Biography,

Geography, and Natural History. Illustrations. 3 Vols. Svo. 106s.

Concise Bible Dictionary. Illustrations. Svo. 21s.

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Christian Antiquities. Comprising the History, Insti-
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Christian Biography, Literature, Sects, and Doctrines;

from the Times of the Apostles to the Age of Charlemagne. Medium Svo,
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Greek and Roman Antiquities. Illustrations. Med. Svo. 28^.
Greek and Roman Biography and Mythology. Illustrations.

3 Vols. Medium Svo. 4i. 4s.

Greek and Roman Geography. 2 Vols. Illustrations.

Medium Svo. 56s.

Atlas op Ancient Geography — Biblical and Classical.

Folio. 61. 6s.

Classical Dictionary op Mythology, Biography, and

Geography. 1 Vol. With 750 Woodcuts. Svo. 18s.
Smaller Classical Dict. Woodcuts. Crown Svo. 7s. 6d.
Smaller Dictionary of Greek and Roman Antiquities.

Woodcuts. Crown Svo. 7s. 6d.

Complete Latin-English Dictionary. With Tables of the

Roman Calendar, Measures, Weights, and Money. Svo. 21s.

Smaller Latin-English Dictionary. New and thoroughly
Revised Edition, 12mo. 7s. 6d.

/>^vC><^A.>«^v.--<CXA^

PUBLISHED BY MR. MURRAY. 27

SMITH'S (Dr. Wm.) ENGLISH COURSE :—

Copious and Critical English-Latin Dictionary. 8vo. 21*.

Smaller English-Latin Dictionary. 12mo. 7s. 6d.

School Manual of English Grammar, with Copious Exercises

and Appendices. Post 8vo. 3s. 6d.

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carefully graduated Parsing Lessons. 16mo. Is.

Manual op English Composition. With Copious Illustra-
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Primary History of Britain. 12mo. 2s. 6d.
School Manual op Modern Geography, Physical and

Political. Post 8vo. 5s.

A Smaller Manual op Modern Geography. 16mo. 25. Qd.

SMITH'S (Dr. Wm.) FRENCH COURSE;—

French Principia. Part I. A First Course, containing a

Grammar, Delectus, Exercises, and Vocabularies. 12mo. 3s. Qd.

Appendix to French Principia. Part L Containing ad-
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French Principia. Part II. A Reading Book, containing
Fables, Stories, and Anecdotes, Natural History, and Scenes from the
History of France. With Grammatical Questions, Notes and copious
Etymological Dictionary. 12mo. 4s. 6d.

French Principia. Part III. Prose Composition, containing

Hints on Translation of English into Frenc}., the Principal Rules of
the French Syntax compared with the English, and a Systematic Course
of Exercises on the Syntax. 12mo. 4s. 6d.

Student's French Grammar. With Introduction by M. Littre

PostSvo. 6s. "^

Smaller Grammar of the French Language. Abridged
from the above. 12mo. 8s. 6d.

SMITH'S (Dr. Wm.) GERMAN COURSE :—

German Principia. Part I. A First German Course, contain-

ing a Grammar, Delectus, Exercise Book, and Vocabularies. 12mo 3s 6d

German Principia. Part IL A Reading Book ; containing
Fables, Anecdotes, Natural History, and Scenes from the History of
Germany. With Questions. Notes, and Dictionary. 12mo. 3s. 6d.

Practical German Grammar. Post 8yo. 3s. 6d.
SMITH'S (Dr. Wm.) ITALIAN COURSE :—

Italian Principia. Part I. An Italian Course, containing a

Grammar, Delectus, Exercise Book, with Vocabularies, and Materials

tor Italian Conversation. 12mo. 3s. 6d.

Italian Principia. Part II. A First Italian Reading Book,

containing Fables, Anecdote?, History, and Passages from the best
Italian Authors, with Grammatical Questions, Notes, and a Copious
Etymological Dictionary. 12mo. 3s. 6d.

SMITH'S (Dr. Wm.) LATIK COURSE:—

The Young Beginner's First Latin Book : Containing the

Rudiments of Grammar, Easy Grammatical Questions and Exercises
with Vocabularies. Being a Stepping stone to Principia Latina, Part l!
for Young Children. 12mo. 2j.

The Young Beginner's Second Latin Book : Containing an

easy Latin Reading Book, with an Analysis of the Sentences, Notes,
and a Dictionary. Being a Stepping-stone to Principia Latina, Part II
for Young Children. 12mo. 2«.

t^-rh-rrr^_aJL -^

28 LIST ^IFlrORKS

i
SMITH'S (Dr. Wm.) Latin Course — continued,

Prinoipia Latina. Part I. Firgt Latin Course, containing a

Grammar, Delectus.and Exercise Book, with Vocabularies. 12mo. 3s, 6d.
*** In this Edition the Cases of the Nouns, Adjectives, and Pronouns
are arranged both as in the ordinary Grammars and as in the Public
School Primer, together with the corresponding Exercises.

Appendix to Prinoipia Latina. Part 1. ; being Additional

Exercises, with Examination Papers. 12mo. 2s. 6d.

Prinoipia Latina. Part II. A Reading-book of Mythology,
Geography, Roman Antiquities, and History. With Notes and Dic-
tionary. 12mo. 3«. 6d.

Prinoipia Latina. Part III. A Poetry Book. Hexametere

and Pentameters; Eclog. Ovidianse; Latin Prosody. 12mo. 3s. 6d.

Prinoipia Latina. Part IV. Prose Composition. Rules of
Syntax, with Examples, Explanations of Synonyms, and Exercises
on the Syntax. 12mo. 3«. 6d.

Prinoipia Latina. Part Y. Short Tales and Anecdotes for

Translation into Latin. 12mo. 3s.

Latin-English Vocabulary and First Latin-English
Dictionary FOR PHiEDRUS, Cornelius Nepos, AND C^SAR. 12mo. 3s. 6d.

Student's Latin Grammar. For the Higher Forms. A new
and thoroughly revised Edition. Post 8vo. 6s.

Smaller Latin Grammar. New Edition. 12mo. 3s. 6d.

Tacitus, Germania, Agricola, and Fir t Book of the

Annals. 12mo, 3 v. 6d.

SMITH'S iDr. Wm.) GREEK COURSE;—

Initia Gr^ca. Part I. A First Greek Course, containing a Gram-
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Appendix to Initia Qjimca. Part 1. Containing additional

Exercises. With Examination Papers. Post 8vo. 2s. 6d.

Initia Gr^sica. Part II. A Reading Book. Containing
Short Tales, Anecdotes, Fables, Mythology, and Grecian History.
12mo. 3«. 6d.

Initia Grjsca. Part III. Prose Composition. Containing the

Rules of Syntax, with copious Examples and Exercises. 12mo. 3s. 6d.

Student's Greek Grammar. For the Higher Forms.

Post 8vo. 65.

Smaller Greek Grammar. 12mo. 35. 6d.
Greek Accidence. 12mo. 2s. 6d.

Plato, Apology of Socrates, &c. With Notes. 12mo. 3.9. 6d,
SMITH'S (Dr. Wm.) SMALLER HISTORIES:—

Scripture History. With Maps and Woodcuts. 16mo.

3."?. 6rf.

Ancient History. Woodcuts. 16mo. 3s. 6c?.
Ancient Geography. Woodcuts. 16mo. 3s. 6d.
Modern Geography. 16mo. 2s. 6d.

Greece. With Coloured Map and Woodcuts. 16mo. 3s. Qd,
Rome. With Coloured Maps and Woodcuts. 16mo. 3s. 6d.
Classical Mythology. Woodcuts. 16mo. 3s. 6d.
England. With Coloured Maps and Woodcuts. 16mo. 35. 6d.
English Literature. 16mo. 3s. 6d.
Specimens op English Literature. 16mo. 3s. 6d,
30MERV1LLE (Mary). Physical Geography. Portrait. Post
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Connexion of the Physical Sciences. Post 8yo. 9s.

PUBLISHED BY MR. MURRAY. 2^

SOMERVITjLE (Mart). Molecular and Microscopic Science.

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SOUTH (John F.). Household Surgery ; or, Hints for Emergen-
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Memoirs of. [See Feltoe.]

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STANHOPE'S (Earl) WORKS :—

History op England from the Reign of Queen Anne to
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Life of William Pitt. Portraits. 3 Vols. 8vo. 36«.

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British India, prom its Origin to 1783. Post 8vo. Zs, 6rf.

History op " Forty-Five." Post 8vo. 3s.

Historical and Critical Essays. Post 8vo. 35. 6rf.

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Life op Belisarids. Post 8vo. 10^. %d.

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pee also Bradley.]
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STEPHENS (Rev. W. R. W.). Life and Times of St. John
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80 LIST OP WORKS

STUDENTS' MANUALS. Post 8vo. 7*. 6d. each Volume :—
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"Woodcuts. Or la 3 parts, price 2s. 6'd. each.
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/History op Modern Europe, from the fall of Constantinople
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Old Testament History ; from the Creation to the Keturn of
the Jews from Captivity. Woodcuts.
New Testament History. With an Introduction connecting
the History of the Old and New Testaments. Woodcuts.
Evidences of Christianity. By H. Wage, D.D. iin the Press.
Ecclesiastical History ; a History of the Christian Church

from its foundation till after the Reformation. By Philip Smith, B.A.
With numerous Woodcuts. 2 Vols. Part I. a.d. 30—1003. Part II.—

1003—1614.

ENaLisH Church History; from the Planting of the Church

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Canon Perry. 2 Vols. First Period, a.d. 596—1509. /Second Period,
1509—1717.

Ancient History of the East ; Egypt, Assyria, Babylonia,
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Woodcuts.

Geography. By Canon Bevan. Woodcuts.

History op Greece ; from the Earliest Times to the Roman

Conquest. By Wm. Smith, D.C.L. Woodcuts,
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History of Rome ; from the Earliest Times to the Establish-
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Gibbon's Decline and Fall of the Roman Empire. Woodcuts.

Hallam's History of Europe during the Middle Ages.

Hallam's History of England ; from the Accession of
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History op France; from the Earliest Times to the Fall
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English Language. By Geo. P. Marsh.
English Literature. By T. B. Shaw, M.A.
Specimens of English Literature. By T. B. Shaw.
Modern Geography ; Mathematical, Physical and Descriptive.

By Canon Bevan, M.A. Woodcuts.

Geography of British India. Political and Physical. By

George Smith, LL.D. Maps.
Moral Philosophy. By Wm. Fleming.

SUMNER'S (Bishop) Life and Episcopate during 40 Years. By

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SWAINSON (Canon). Nicene and Apostles' Creeds; Their

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Athanasius." Svo. 16s.

SWIFT (Jonathan). [See Craik.]

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()— oO\--fe--t>o4 "^/^^'i^^Ay^^ O^

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Date Due

All library items arc subject to recall 3 weeks from
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